DOI: 10.31038/NAMS.2020316

 

The research areas in the science and engineering have been looking to develop new advance materials for energy technologies, which have the capability of improving life in the world. Globally carbon dioxide emission from fossil fuel combustion increases faster than expected, because of inefficiency in fuel and the weakening of natural carbon sinks.The major source of carbon emissions is the burning fossil fuels and other natural sources. It was observed that nanotechnology able to decrease the need for fossil fuels, thus having a positive impact on global warming. Nanotechnology and its products (or nanomaterials) mostly involve in the applications of renewable energies (such as, solar and hydrogen fuel cells and energy storage device), which result in nearly zero Co2 emissions. Increasing the use and efficiency of renewable/ecofriendly energy resources will overcome the use of burning fossil fuel, and at the same time decreasing the consumption of current fuels is one way to slow down and ultimately stop global warming. The advance development in nanomaterials is still in progress, which can economically absorb the carbon dioxide from the air, capture toxic pollutants from water and degrade solid waste into useful products. Nanomaterials are efficient catalysts and mostly recyclable.

(1) Advance Nanomaterials for Energy Storage applications:

Hydrogen today is enjoying unprecedented state in the world in emerging fields of renewable energy by substitution of fossil fuels (i.e. petroleum, natural gas and coal), which meet most of the world’s energy demand today, are being depleted fast. Combustion products of fossil fuel are creating global problems (global warming, climate change, ozone layer depletion, acid rain, oxygen depletion and pollution), which posing great danger for our environment and eventually for life on our planet. Scientists all over the world agree to replace the existing fossil fuel system with the Hydrogen Energy System. Hydrogen is the fuel of 21st century because of it being light, most abundant, storable, energy-dense, and produces no direct emissions of pollutants or greenhouse gases. Hydrogen energy has potential to solve energy problems of the planet earth giving it a sustainable and safe future, resulting into a clean planet. H2 storage and release is a key challenge which is solved by metal hydrides which can absorb hydrogen in atomic form and release it easily by raising their temperature or pressure. Lots of important advances have been resulted during last one decade for developing nanostructure materials with high volumetric and gravimetric hydrogen capabilities. There is an urgent need to developed low cost, safe and inexpensive nanostructured hydride materials having high hydrogen content and fast desorbing properties at low temperature and pressure. In the present energy scenario, most of hydrogen storage materials have storage capacities not more than 5 wt% which is not satisfactory for practical application as per DOE USA Goal. Many research groups are currently working on hydrogen storage material to get best de/absorption kinetics with ultimate H2 contents. e.g. Mg hydride is a promising hydrogen storage material with reversible hydrogen capacity up to 7.6 wt% for on board applications with fast kinetics, good cycle life and decreased hydrogen desorption temperature. Good hydrogen storage properties are possible by introducing enough catalyst and by ball milling which introduces defects with improved surface properties. Hence lot of research work is needed for improving metal hydrides properties such as hydrogenation, fast charging / discharging rate, fast kinetics, thermal and cyclic behaviour. All over the world serious type of research and development work is going on Hydrogen Energy. Internal combustion engines are being modified for hydrogen fuel. Efficient fuel cells are being developed to convert hydrogen efficiently to electricity. Research and development work on metal hydride refrigeration and air conditioning systems is in advance stages and will be available for commercial applications shortly. Hydrogen fuel subsonic and supersonic transport planes are already in their test runs,In fact hydrogen shows the solution and is capable of the progressive and non-traumatic transition of today’s world energy scenario to feasible, safe, reliable and completely sustainable energy future. Scientists are advocating use of hydrogen for all types of energy applications which was earlier possible only by fossil fuel and they have hoped for the international response to the global climate change. Hence there are enough environmental and public health benefits of direct use of hydrogen energy and justifying for moving ahead, based on what we already know about fossil fuels and their consequences.

(2) Advance Nanomaterials for Solar Cell Applications:

Solar cell materials are the current prospects for clean energy research to offering strong power outputs from low-cost raw materials that are relatively simple to process into working devices. Although the potential of the material (Perovskite based solar cells) is just starting to be understood, it has caught the attention of the world’s leading solar researchers are trying to commercialize it.e.g. organic-inorganic lead halide perovskite solar cells are contenders in the drive to provide a cheap and clean source of energy with electrical power conversion efficiencies of over 29%. The high efficient photovoltaic materials are recognized for optically high absorption characteristics and balanced charge transport properties with long diffusion lengths. Nevertheless, there are lots of puzzles to unravel to understand the fundamental basis of such advance materials. Perovskite solar cells (PSC) are economically viable from a viewpoint of efficiency, however, commercialization is still challenging because of the toxicity of lead, long term stability, and cost-effectiveness. Future research directions will benefit from finding lead-free light-absorbing materials. However, the reported efficiencies are thus far too low to commercialize PSC’s. The cost-effectiveness of the raw materials and the fabrication processes is a significant issue. High throughput fabrication strategies with reproducible materials and processes should be developed. Moreover, mechanical functionalities such as flexibility, stretchable and long term stability properties will lead to making PSC’s more economically viable.

DOI: 10.31038/NAMS.2020315

Abstract

Cyber hybrid warfare has been known since antiquity, it is not a new terminology nor a new practice. It can have an effect even more than a regular conventional war. The implementation of the cyber hybrid war aims to misinform, guide and manipulate citizens, disorganize the target state, create panic, overthrow governments, manipulate sensitive situations, intimidate groups, individuals and even shortened groups of the population, and finally to form an opinion according to the enemy’s beliefs. Creating online events designed to stimulate citizens to align with the strategy of governments or the strategy of the enemy government is a form of cyber hybrid warfare. The cyber hybrid warfare falls under the category of asymmetric threats as it is not possible to determine how, and the duration of the cyber invasion.The success or not of a cyber hybrid war depends on the organization, the electronic equipment, and the groups of actions they decide according to the means at their disposal to create the necessary digital entities. Finally, the cyber hybrid warfare is often used to show online military equipment aimed at downplaying its moral opponent.

Introduction

The cyber hybrid warfare also includes DeepFake, a practice mentioned in Christos Beretas previous research. The cyber hybrid war aims to disrupt and hurt the adversarial state in an organized and targeted manner, mainly regarding the organizational structure of the target state and its functioning.Digital media are used to intimidate citizens, target specific groups of people, disseminate false news between political and military leadership in order to spread hatred and resentment on both sides, to divide the people, and finally the fall of the government, followed by the anger and indignation of the people. The cyber hybrid warfare is not only and exclusively applied during a period of natural war, it is a kind of war that can be waged for years and of course in times of peace. It is difficult for citizens in a cyber hybrid war to understand the truth and lies.A well-organized cyber hybrid war is difficult for people to recognize as the facts presented are so convincing that it is impossible to recognize them as false. The ways to avoid and protect against such a war are numerous and require knowledge, experience, alertness, high morale, courage and professionalism to deal with such a cyber threat from its birth.Sovereign states around the world are using the cyber hybrid warfare to blackmail, trap, mislead, both foreign governments and citizens, achieving remote results without the use of physical violence and natural disasters. The cyber hybrid war has come to stay, and it is an emerging form of war – the pressure of the strong against the weak or better of the organized states against the disorganized. As mentioned above, a great DeepFake video is capable of stirring up enormous panic and hatred in a society. It is an asymmetric threat that is increasing day by day.

Characteristics

The cyber hybrid war is an asymmetric threat that is defined when an entity uses electronic means to disturb the peace or spread panic in the target state and launch hostilities or uproot social groups residing in it. A fake video, for example, that will be sent to targeted social groups is capable of sparking riots in the crowd with demonstrations and violence. By reading this one can easily understand the reader that the cyber hybrid war is the result of an entity preceding its onset.This entity is the digital asymmetric threat which if not handled properly then evolves into a cyber hybrid war. The cyber hybrid war is not tantamount to an isolated practice, that is, it is not a common attack on the adversarial state; rather, it consists of organized methods that are often impossible to identify, such an attack may include social media, online press, videos and hostilities from different events, etc.The difference between a cyber hybrid war and conventional warfare is that except there are no killings and conflicts, there is a constant low-level influx of information affecting the target state. That is, it does not follow the logic that an event has occurred, a number of people have risen and then the digital invasion process has ended, on the contrary, the digital presence is continuous and stable at the same level as possible.

Advanced stages of a cyber hybrid war include practices such as misinformation aimed at the financial loss of the target state, intra-country turmoil from pro-country groups that launched the cyber hybrid war to compel its citizens to withdraw. for the purpose of financial loss or even the overthrow of the government.In a cyber hybrid war, the invaders’ practical ways of attacking are not one-sided but two-sided, which means that in one field they can decrease and increase in another, for example a false bent can be seen in social media news and on the contrary the volume of fake videos is growing too.A cyber hybrid war is often won when combine electronic and physical attacks in the target state, which means that in the target state it requires the penetration of disturbing elements in order to revolt and destroy the target state’s infrastructure and economy.This includes increasing crime, which will then be used in the media and social media by the adversary state as a means of corrupting the target country with the ultimate aim of reducing its reputation, spreading fear to other countries. aimed at restricting travelers, other countries’ security reviews, further financial burden, withering and global isolation.

The success or not of a  cyber hybrid war in addition to the proper organization, hardware, and staff, requires and sufficient funding for the whole venture, funding is a key success factor, with insufficient funding the result will be the opposite, as it will unprofessionalism has emerged, and it is easy for social groups to understand that this is fake news, which is equivalent to project failure and redesign.Funding can come exclusively from the state that organizes the cyber hybrid threat, it can come from friendly countries in it, as well as from organizations that are scattered around the world, usually when a cyber hybrid war is funded by organizations around the world, the communication takes place through social media or smart phone applications that offer anonymous messaging services. At this point it should be noted that there is no formal single practice or specificity in the form of steps that need to be taken to be considered a threat as a cyber hybrid threat, so there is no legal framework defining the steps that characterize that this is a threat to the target state to take legal actions, the legal framework is incomplete and that is something that countries that are waging such wars are very aware of and they are washed.

As technology evolves, asymmetric threats increase as states with sufficient funding and equipment are able to wage such wars on a large scale, which is why the cyber hybrid wars will intensify. That is why governments and security agencies around the world are trying to organize and shield themselves against the cyber hybrid war, now knowing that its impact is greater than even conventional warfare.Preparing, organizing, and preventing such attacks are the basic prerequisites for dealing with the threat. This entails writing and implementing a cyber security policy that outlines the conditions, steps to be taken, education, definitions, and how to handle such incidents.The security policy should be updated annually and adapted to the needs and the level of risk that exists per period. It must adequately specify how government agencies must act in a period of digital asymmetric threat. Allied countries need to formulate a common cyber policy so that dealing with a digital asymmetric threat is unified. It is of no use to allies and friendly countries not to implement a common strategy against digital asymmetric threats. Friendly organized countries can easily trap the enemy and destroy the plans.

Conclusion

The cyber hybrid war is made up of several entities that, depending on the smooth functioning of all entities, are judged to be successful or unsuccessful. It is an asymmetric threat, no one can know the length or the size of the area it will take place. It is a kind of war that with the development of technology will see significant development. An important factor in success is financial support and therefore the amount of money each state is willing to spend to design and implement a credit cyber hybrid war. A well-organized and implementable cyber hybrid warfare can cause severe damage to a conventional one. It is not necessary for a cyber hybrid war to be designed exclusively by wealthy and developed countries, such a war can be created by any state that has the knowledge, money, and organization to mount an asymmetric threat. In the cyber hybrid war, the chances of convicting states for war crimes are minimized, as in the cyber hybrid war there is no clear legal framework defining the methods of intruders.Identifying a digital threat is difficult due to the complexity of its actions; identifying and neutralizing a cyber hybrid threat requires knowledge and experience of such threats. Some countries in the world have developed methods and teams to detect and manage such threats, but the measures they take to protect them are found to be incomplete and not fully effective and the reason is the rapid development of technology that new methods and techniques are constantly being discovered.Finally, as has been said above, the best defense is the organization of friendly states to provide a single aid and formulate a unified security policy that will lead to massive isolation of cyber hybrid threats. Unified repression by friendly countries against such attacks is the best organized defense against hybrid threats.

References

1. Christos Beretas(2020)DeepFake – Another One Cyber Threat.
2. Andreas Krieg, Jean-Marc Rickli(2019) Surrogate Warfare: The Transformation of War in the Twenty-First Century.
3. Andrew Fevery(2018) Hybrid Warfare.

DOI: 10.31038/NAMS.2020314

Opinion Article

This article is a personal opinion article and nothing more.

We are all living in the last days a state of panic wherever we are in the world. This panic is justified and owe it to the well-known Coronavirus pandemic (COVID-19) as it is officially called. The virus causes from mild to very severe symptoms, such as acute respiratory infection, that is, ARF pneumonia(AcuteRespiratoryFailure). Symptoms of the virus start from a cough, fever with tithing slowly, tiredness, and shortness of breath.

So far there is no vaccine or antibody that kills the virus. The treatments are based on antibodies created to treat the flu and pneumonia. Experimental tests of cocktail antibiotics are also used which act on a case-by-case basis in conjunction with the patient’s physical condition, concomitant illness, and age.

The way of virus actions have triggered a number of questions that I’m sure they will be of concern to you, whether you have been involved or have not found answers Important questions remain unanswered, such questions are:

• The first patient how has been infected by the virus?

• In the country where the virus first appeared, did they allow the sale of animals that had been used as experimental animals before?

• Is allowed  to sell laboratory cloned animals?

• Is it permissible to import from outside of the country laboratory created cloned animals?

• Is there evidence that animals or seafood , have the virus spread or been infected?

• Are there any announcements or publications from government sources about the study, safety and protection against such corona-viruses in the past?

• Does virus analysis show mutations based on the corona-virus structure?

Focusing on time actions of the virus, again causes questions, ranging from 2 to 14 days with an average of 5 days. Sound like the virus have hooks and try to get into the human body. By adding amino acids, a virus that could threaten humans could easily mutate.

Sound like the virus enters the human body, and after it enters, stays there and shows signs of existence after a few days, this could be concealed in such a way to protect itselfto not detected and kill it early before infect the human body, also by this way may hide the exact date of infection, so that the place of infection is not easily detected.

Analyzing the above reminds me a bit of the way HIV works, where after about a week those infected with HIV show flu or simply cold symptoms, then the symptoms subside and the carrier stays asymptomatic for years, spreading ignorant the virus.

Considering all of the above, to behave the way COVID-19 might behave, this virus may be made in the laboratory, as a biological weapon that was either accidentally escaped, or applied as a test under real conditions, or for some purpose, by whom; unknown.People who believe it is a biological weapon could think of two scenarios, the first being a real-life test, and the second being that the virus escaped from a laboratory by accident in an experimental animal or a worker.

Whatever the reality is, I hope very soon all of this will be over and everything will return to normal in our lives.

References

1. PhD Candidate in Cyber Security (Innovative Knowledge Institute) Paris, France.
2. Member of Alpha Beta Kappa Honor Society, Alpha of Ohio, USA.

DOI: 10.31038/NAMS.2020313

Abstract

The textile wastewaters could not be treated effectively with conventional treatment processes due to high polyphenol and aromatic compounds and colour content. In this study, by doping of NiCO₂O₄ to  Bi₂O₂CO₃ the generated NiCO₂O₄to Bi₂O₂CO₃nanocomposite was used for the photocatalytic oxidation of COD components (COD_total, CODdissolved, COD_inert), color, organophenols and organoaromatic compounds from a textile industry wastewaters (TW) at different operational conditions such as, at different photooxidation times (5 min, 15 min, 30 min, 60 min, 80 min and 100 min), at diferent NiCO₂O₄ratios (0.5wt% , 1wt%, 1.5wt%, 2wt%), at different NiCO₂O₄ / Bi₂O₂CO₃nanocomposite concentrations (1, 5, 15, 30 and 45 mg/L), under 10, 30, 50 and 100 W solar irradiations, respectively. The maximum COD_total, COD_inert, total flavonols, total aromatic amines (TAAs) and color photooxidation yields were 99%, 92%, 91%, 98% and 99% respectively, under the optimized conditions, at 30 mg/L Ni/BiO nanocomposite with a Ni mass ratio of 1.5 wt% under 50 W UV (ultraviolet) light, after 60 min photooxidation time, at 25°C. The photooxidation yields of kaempferol (KPL), quercetin (QEN), patuletin (PTN), rhamnetin (RMN) and rhamnazin (RHAZ) from flavonols and 2-methoxy-5-methylaniline (MMA), 2,4-diaminoanisole(DAA); 4,40-diamino diphenyl ether (DDE), o-aminoazotoluene (OAAT), and 4-aminoazobenzol (AAB) from polyaromatic amines were > 82%.The pollutants of textile industry wastewater were effectively degraded with Ni doped BiO nanocomposite.

Keywords

Flavonols; Nickel cobaltite NiCO₂O₄ nanocomposite; bismuth subcarbonate (Bi₂O₂CO₃) nanocomposite; Photooxidation; Polyaromatic amines; Ultraviolet (UV) light irradiation.

Biographical notes

Delia Teresa Sponza is a Professor at the Department of Environmental Engineering, Engineering Faculty, Dokuz Eylül University,İzmir, Turkey. She graduated her MSc and PhD degrees from Dokuz Eylül University, Turkey, in Environmental Engineering. Her research interests are environmental microbiology,environmental sciences and toxicity. She has published a number ofresearch papers at the national and international journals.

Rukiye Oztekin is a Researcher at the Department of Environmental Engineering, Engineering Faculty, Dokuz Eylül University, İzmir, Turkey. She graduated her MSc and PhD degrees from Dokuz Eylül University, Turkey, in Environmental Engineering. Her research interestsinclude environmetal sciences and toxic industrial wastewater treatment.

Introduction

Textile industry is one of those industries that consume large amounts of water in the manufacturing process [1] and, also, discharge great amounts of effluents with synthetic dyes to the environment causing public concern and legislation problems. Synthetic dyes that make up the majority (60–70%) of the dyes applied in textile processing industries [2] are considered to be serious health risk factors. Apart from the aesthetic deterioration of water bodies, many colorants and their breakdown products are toxic to aquatic life [3] and can cause harmful effects to humans [4,5]. Several physico-chemical and biological methods for dye removal from wastewater have been investigated [6-8] and seem that each technique faces the facts of technical and economical limitations [7]. The traditional physical, chemical and biologic means of wastewater treatment often have little degradation effect on this kind of pollutants. On the contrary, the technology of nanoparticulate photodegradation has been proved to be effective to them. Compared with the other conventional wastewater treatment means, this technology has such advantages as: (1) wide application, especially to the molecule structure-complexed contaminants which cannot be easily degraded by the traditional methods; (2) the nanoparticles itself have no toxicity to the health of our human livings and (3) it demonstrates a strong destructive power to the pollutants and can mineralize the pollutants into carbondipxide (CO₂) and water (H₂O) [9].

Bi₂O₂CO₃ has gained much attention due to its promising photocatalytic activity for wastewater treatment [10-12]. Although Bi₂O₂CO₃ has been widely studied in the photocatalytic degradation of wastewater, little attention has been poured to investigate the microwave catalytic performance of Bi₂O₂CO₃ for microwave catalytic oxidation degradation of wastewater, up to now. At the same time, the magnetic NiCO₂O₄ has intriguing advantages, such as excellent microwave absorption performance, low cost, magnetically separable property, and high stability [13]. To the best of our knowledge, NiCO₂O₄-Bi₂O₂CO₃ composite as microwave catalyst for degradation o more semiconductor photocatalysts have been found to be capable of photocatalytic degradation of organic macromolecular contaminants in wastewater [14, 15]. Therefore, photocatalytic degradation has become the most environmentally friendly, energy-saving, and efficient water pollution treatment method. In view of the fact that the traditional photocatalysts (such as TiO₂) have large band gap energy and low response to visible light, their application is greatly limited. Among these miconducting photocatalysts, bismuth molybdate (Bi₂MoO₆) as a ternary oxide compound of Aurivillius phase becomes one of the promising materials. This is because it has a unique layered structure sandwiched between the perovskite octahedral (MoO₄)₂⁻sheets and bismuth oxide layers of (Bi2O₂)²⁺ [16-18]. Its dielectric property, ion conductivity, and catalytic performance have obvious advantages in bismuth-based semiconductors [19, 20]. Nevertheless, the light absorption property of the pure Bi₂MoO₆ primarily appears in the ultraviolet light region, which is only a small part of the solar spectra. Meanwhile, it presents a high recombination rate of electronhole
pairs in the process of photocatalytic reaction [21]. Therefore, researchers have improved the performance of Bi₂MoO₆ by means of
morphology controlling, semiconductor compounding, and doping modification [22]. Among these measures, doping has proven to be an effective method to ameliorate the surface properties of photocatalysts and enhance photocatalytic performance.

It was reported that carbon-doped Bi₂MoO₆ exhibited significantly enhanced and stable photocatalytic properties compared with Bi₂MoO₆ [23], which carbon replaced the O₂⁻anion in the lattice of Bi₂MoO₆, resulting in lattice expansion and grain diameter reduction, enhancement of specific surface area [24]. prepared Graphene-Bi₂MoO₆ (G-Bi₂MoO₆) hybridphotocatalysts by a simple one-step process, and an increase in photocatalytic activity was observed for G-Bi₂MoO₆ hybrids compared with pure Bi₂MoO₆ under visible light. Xing et al., (2017) reported the photocatalytic activity of 0.5% Pd–3C/BMO was robustly enhanced about 5-fold for Rhodamine B (RhB) degradation within 40 min under UV + visible light irradiation and 29-fold for O-phenylphenol (OPP) degradation within 120 min under visible light irradiation in comparison with pristine Bi₂MoO₆, respectively. [25] prepared a B-doped Bi₂MoO₆ photocatalyst with hydrothermal method by using HBO₃ as a dopant source. It was found that B-doping increases the amount of Bi⁵⁺ and oxygen vacancies, so that the visible light absorption of catalyst is stronger, and the band gap energy is lower, which significantly improves the photocatalytic activity of Bi₂MoO₆. [26] successfully synthesized sulfur-doped copper-cobalt bimetal oxide by coprecipitation method, which significantly improved the catalytic performance and stability of the catalyst. [27] fabricated Bi₂MoO₆ surface co-doped with Ni²⁺ and Ti⁴⁺ ions through an incipient-wetness impregnation technology and calcination method, with the results suggesting Ni²⁺ and Ti⁴⁺ codoping increases visible-light absorption by Bi₂MoO₆ and promotes the separation of photogenerated charge carriers. Density functional theory calculations and systematical characterization results revealed that Biself-doping could not only promote the separation and transfer of photo generated electron-hole pairs of Bi₂MoO₆ but also alter the position of valence and conduction band without changing its preferential crystal orientations, morphology, visible light absorption, as well as band gap energy [28, 29] synthesized pure and various contents of Ce³⁺ doped Bi₂MoO₆ nano structures by a facile hydrothermal method. The 0.5%Ce³⁺ doped Bi₂MoO₆ exhibitsthe best photocatalytic activity of 96.6% within 20 min for RhB removal.

The photocatalytic performance of NiCO₂O₄-doped Bi₂MoO₆ nanoparticles has not been investigated extensively for the removals of aromatics and polyphenols from a textile industry. In this work, the phsicochemical properties of NiCO₂O₄ doped Bi₂O₂CO₃ nanocomposite was investigated using microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), photoluminescence spectra (PL), N2 adsorption–desorption, elemental mapping, Raman and diffused reflectances pectra (DRS) analysis. The photocatalytic oxidation of pollutant parameters [COD components (COD_total, CODdissolved, COD_inert), flavonols (kaempferol, quercetin, patuletin, rhamnetin and rhamnazin), polyaromatic amines (2-methoxy-5-methylaniline, 2,4-diaminoanisole, 4,40-diamino diphenyl ether, o-aminoazotoluene, and 4-aminoazobenzol) and color] from the TW at different operational conditions such as, at increasing photooxidation times (5 min, 15 min, 30 min, 60 min, 80 min and 100 min), at diferent Ni mass ratios (0.5wt% , 1wt%, 1.5wt%, 2wt%), at different Ni-BiO photocatalyst concentrations (1, 5, 15, 30 and 45 mg/L), at different pH ranges (4, 6, 8, 10) under 10, 30, 50 and 100 W UV light irradiations, respectively, were investigated .

Materials and methods

Raw wastewater

The characterization of raw TW was given in Table 1.

Table 1. Characterization values of TW at pH=5.7 (n=3, mean values ± SD). (SD: standard deviation; n: the repeat number of experiments in this study).

Chemical structure of flavonols and poliaromatics present in the TW

The structure of flavonols in the TW was shown in Figure 1. The structure of polyaromatics in the TW was given Figure 2.

Figure 1. Chemical structure of flavonoids in the TW.

Figure 2. Chemical structure of polyaromatics in the TW

Preparation of photocatalysts

Ni-doped BiO nano particles were prepared by co-precipitation method using nickel nitrate hexahydrate [Ni(NO₃)₂.6H₂O] (Analytical grade, Merck ) and Bismuthnitrate hexahydrate [Bi(NO₃)₂·6H₂O] (Sigma, Aldrich) as the precursors of nickel and bismuth, respectively. Ni(NO₃)₂.6H₂O and sodium carbonate anhydrous (Na₂CO₃) were dissolved separately in double distilled H₂O to obtain 0.5 mol/Lsolutions. Nickel nitrate solution (250 mL of 0.5 mol/L) was slowly added into vigorously stirred 250 mL of 0.5 mol/L Na₂CO₃ solution. Nickel nitrate in the required stoichiometry was slowly added into the above solution and a white precipitate was obtained. The precipitate was filtered, repeatedly rinsed with distilled H₂O and then washed twice with ethanol. The resultant solid product was dried at 100°C for 12 h and calcined at 300°C for 2 h. BiO particles were also prepared by the same procedure without the addition of nickel nitrate solution. The doping Ni mass ratios of Bismuth are expressed as wt%.

X-Ray diffraction (XRD) analysis

XRD patterns of the samples are going to carry out using a D/Max-2400Rigaku X-ray powder diffractometer operated in the reflection mode with Cu Ka (λ = 0.15418 nm) radiation through scan angle (2θ) from 20° to 80°.

Scanning electron microscopy (SEM) analysis

The morphological structures of the Ni-BiO nanocomposites before photocatalytic degradation with UV light irradiations and after photocatalytic degradation with UV by means of a SEM.

Fourier transform infrared spectroscopy (FTIR)analysis

The FTIR spectra of Ni, BiO and Ni-BiO samples were measured with FTIR spectroscopy measurements.

Photocatalytic degradation reactor

A 2 L cylinder kuvars glass reactor was used for the photodegradation experiments in the TW under different UV powers, at different operational conditions. 1000 mL TW was filled for experimental studies and the photocatalyst were added to the cylinder glass reactor. The photocatalytic reaction was operated with constant stirring during the photocatalytic degradation process. 10 mL of the reacting solution were sampled and centrifugated (at 10000 rpm) at different time intervals.

Used chemicals

Ni(NO₃)₂.6H₂O (Analytical Grade, Merck, Germany) and Bi(NO₃)3·6H₂O (Analytical grade, Merck, Germany) were used as nickel and bismuth sources, respectively. Na₂CO₃ was purchased from Merck (Analytical grade). Helium, He(g) (GC grade, 99.98%) and nitrogen, N₂(g) (GC grade, 99.98%) was purchased from Linde, (Germany). Kaempferol (99%), quercetin (99%), patuletin (99%), rhamnetin (99%), rhamnazin (99%), 2-methoxy-5-methylaniline (99%), 2,4-diaminoanisole (99%), 4,40-diamino diphenyl-ether (99%), o-aminoazotoluene (99%), 4-aminoazobenzol (99%) were purchased from Aldrich, (Germany).

Analytical methods

pH, T(°C), ORP, DO, BOD5, COD_total, CODdissolved, total suspended solids (TSS), Total-N, NH₃-N, NO₃-N, NO₂^–N, Total-P and PO₄-P measurements were monitored following the Standard Methods 2310, 2320, 2550, 2580, 4500-O, 5210 B, 5220 D, 2540 D, 4500-N, 4500-NH3, 4500-NO₃, 4500-NO₂ and 4500-P [30]. Inert COD was measured according to glucose comparison method [31]. The samples were analyzed by high pressure liquid chromatography (HPLC) with photodiode array and mass spectrometric detection using an Agilent 1100 high performance liquid chromatography system consisting of an automatic injector, a gradient pump, a Hewlett–Packard series 1100 photodiode array detector, and an Agilent series 1100 VL on-line atmospheric pressure ionization electrospray ionization mass spectrometer to detect flavonols namely kaempferol, quercetin, patuletin, rhamnetin, rhamnazin and polyaromatics namely, 2-methoxy-5-methylaniline, 2,4-diaminoanisole, 4,40-diamino diphenyl-ether, o-aminoazotoluene, 4-aminoazobenzol, respectively. All the  metabolites were measured in the same HPLC by mass spectrometric detections. Operation of the system and data analysis were done using ChemStation software, and detection was generally done in the negative ion [M − H]– mode, which gave less complex spectra, although the positive ion mode was sometimes used to reveal fragmentation patterns—especially patterns of sugar attachment. Separation of flavonol components was made on a Vydac C18 reversed phase column (2.1 μm dia. × 250 mm long; 5-μm particle size). Columns were eluted with acetonitrile-water gradients containing 0.1% formic acid in both solvents. The quality of the raw (un-treated) and photooxidated wastewater were determined by measuring the absorbances of the supernatans at wavelengths varying between 200 nm, 250 nm, 300 nm, 350 nm and 540 nmusing an Aquamate Termoelectron Corporation UV-vis spectrophotometer.

Measurement of photonic efficiency (lr) of Ni doped BiO

The relative photonic efficiency of the catalyst is obtained by comparing the photonic efficiency of Ni-doped BiO with that of the standard photocatalyst (BiO). In order to evaluate lr, a solution of 1-Methylcyclopropene-MCP (40 mg/L) with a pH of 10 was irradiated with 100 mg of BiO and Ni-doped BiO for 60 min. From the degradation results, Ir was calculated as follows (Eq. 1).

Operational conditions

Under 10-30-50 and 100 W  UV light powers the photocatalytic oxidation of the pollutant parameters in the TW at different operational conditions such as at increasing Ni mass ratios in the Ni-BiOnanocomposite(0.5wt% , 1wt%, 1.5wt%, 2wt%), at increasing photooxidation times (5 min, 15 min, 30, 60 min, 80 min and 100 min), at different Ni-BiOphotocatalyst concentrations (1, 5, 15, 30 and 45 mg/L), under acidic, neutral and basic conditions, respectively.

All the experiments were carried out following the batch-wise procedure. All experiments were carried out three times and the results were given as the means of triplicate sampling with standard deviation (SD) values.

Results and analysis

XRD Analysis results

The powder XRD patterns of BiO and Ni-doped BiO with different lanthanum mass ratios are shown in Figure 3. The XRD patterns of all the Ni-doped BiO catalysts are almost similar to that of BiO, suggesting that there is no change in the crystal structure upon Ni loading. This also indicates that Ni⁺² is uniformly dispersed on BiO nanoparticles in the form of small Ni2O₂ cluster. However the Ni-doped samples have a wider and lower intense diffraction peaks than pure BiO. Moreover, the XRD peaks of Ni-doped BiO continuously get broader with increasing the Ni loading up to a mass ratio of 2%wt.

Figure 3. XRD patterns of BiO and Ni doped BiO (a) pure BiO, (b) 2 wt% Ni doped BiO, (c) 0.5wt% Ni doped BiO, (d) 1.0wt% Ni doped BiO, and (e) 1.5wt% Ni doped BiO.

SEM Analysis results

The morphology of nanocomposite particles is analyzed by SEM. Figure 4 shows that the nanocomposite material is partly composed of clusters containing composite nanoparticles adhering to each other with a mean size of around 20-80 nm before photooxidation process (Figure 4a) while the size increased to 24-86 nm after photooxidation (Figure 4b) with intermediates and remaining not photodegraded pollutants.

Figure 4. SEM micrographs of pure and nickel modified BiO, (a) pure BiO at 25°C, (b) Ni doped BiO at 25°C.

FTIR Analysis results

Figure 5 shows the FTIR spectrum of BiO and Ni-doped BiO, BiO powder synthesized under laboratory conditions. The peak between 400 and 700 cm^-1 give the information of Bi–O and Ni–Bi–O on the FTIR spectra. The peak at 437–455 cm^-1 give the information about stretching vibration of crystalline hexagonal zinc oxide (Bi–O stretching, vibration) and the peaks from 902 to 1020 cm^-1 are attributed to the bond between lanthanum and oxygen (Ni–O). The broad peak between 3400 to 3900 cm^-1 indicate the OH groups, due to the H₂O which indicates the existence of atmospheric H₂O adsorbed on the surface of nanocrystalline powder. An absorption band and a peak have been observed at 2350 cm^-1, respectively, which arises from the absorption of atmospheric CO₂ on the metal cations.

Figure 5. FTIR Spectra of pure BiO and Ni-doped BiO nanoparticles, with different concentration of dopant

Results and Discussions

Effect of increasing Ni-BiOnanocomposite concentrations on the removals of TW pollutants

The effects of increasing Ni-BiO nanocomposite concentrations (1 mg/L, 5 mg/L, 15 mg/L, 30 mg/L and 45 mg/L), on the photocatalytic oxidation of polutant parameters in the TW was investigated. The preliminary studies showed that the maximum removal of COD with 20 mg/L Ni-BiO nanocomposite was 89% with 70 min photooxidation time at pH=7.8 with 40 W UV power (Data not shown). Based on these yields the operational conditions for photocatalytic time were choosen as 60 min at a power of 50 W and at a pH of 8. The maximum photocatalytic oxidation removals for all pollutants in the TW were observed at 30 mg/L Ni-BiO nanocomposite concentrations, at pH=8.0, after 60 min photooxidation time and at 25°C at a power of 50 W (Figure 6). Removal efficiencies slightly decreased at 45 mg/L Ni-BiO nanocomposite concentration, because over load of surface area of Ni-BiO nanocomposites (Figure 6). This limiting the power of UV irradiation. Lower photo-removal efficiencies was measured for 1, 5, and 15 mg/L Ni-BiO concentrations due to low surface areas in the nanocomposite. On the contrarily, the surface area is high at 30 mg/L Ni-BiO nanocomposite concentrations. Therefore, the maximum photodegradation yield was observed in this nanocomposite concentration. The COD_total, COD_inert, total flavonols, total aromatic amines and color removals increased linearly as the Ni-BiO nanocomposite concentrations were increased from 1 mg/L up to 5 mg/L, to 15 mg/L, and up to 30 mg/L, respectively (Table 2 and Figure 6). Furher increase of nanocomposite concentration to 45 mg/L affect negatively the all the pollutant yields. The reason for this is the optimum amount of catalyst increases the number of active sites on the photocatalyst surface, which in turn increase the number of OH^● and superoxide radicals (O₂^– ●) to degrade pollutant parameters (COD components, flavonols, polyaromatics, color). When the concentration of the catalyst increases above the optimum value, the degradation decreases due to the interception of the light by the suspension [32]. reported that as the excess catalyst (turbidity) prevent the illumination of light, OH^●, a primary oxidant in the photocatalytic system decreased and the efficiency of the degradation reduced accordingly. Furthermore, the increase in catalyst concentration beyond the optimum may result in the agglomeration of catalyst particles; hence, the part of the catalyst surface becomes unavailable for photon absorption, and thereby, photocatalytic oxidation efficiency decreases [33]. Maximum COD_total, COD_inert, total flavonols, TAAs and color removal efficiencies were obtained after 60 min photooxidation process with yields of 99%, 92%, 91%, 98% and 99%, respectively, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration at 50 W power and at 25°C (Figure 6). Flavonols such as kaempferol, quercetin, patuletin, rhamnetin, rhamnazin removal efficiencies were 87%, 88%, 90%, 87% and 85% respectively, after 60 min photooxidation time, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration and at 25°C temperature (Table 2). Polyaromatic amines such as, 2-methoxy-5-methylaniline, 2,4-diaminoanisole, 4,40-diamino diphenyl ether, o-aminoazotoluene, 4-aminoazobenzol removal efficiencies after photooxidation process were 93%, 95%, 87%, 84% and 82%, respectively, after 60 min photooxidation time, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration at 50 W  UV power and at 25°C (Table 2).

Figure 6. Removal efficiencies of COD_total, COD_inert, total flavonols and TAAs at Ni-BiO=1 mg/L, BiO=5 mg/L, BiO=15 mg/L and BiO=30 mg/L.

Table 2. Effect of increasing Ni-BiO nanocomposite concentrations on the TW during photooxidation process after 60 min, at 50 W UV irradiation, at pH=8.0, at 25°C.

Kaempferol metabolies such as, 3-O-[2-O,6-O-bis(α-L-rhamnosyl)-( β-D-glucosyl] quercetin, 3-O-[6-O-(α-L -rhamnosyl)-( β-D-  glucosyl]quercetin, 3-O-{2-O-[6-O-(p-hydroxy-trans-cinnamoyl)-{ )-, β-D-glucosyl]- á-L-rhamnosyl}kaempferol decreased from 5.7 mg/L to 0.86 mg/L, from 5.7 mg/L to 1.08 mg/L, from 5.7 mg/L to 1.25 mg/L, respectively, after 60 min photooxidation time, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration at 50 W  UV power and at 25°C (Table 3). Quercetin metabolites such as, 3-O-[6-O-( α-L -rhamnosyl)- )-(β-D-glucosyl]quercetin, 3-O-{2-O-[6-O-(p-hydroxy-trans-cinnamoyl)-( β-D -glucosyl]– á-L-rhamnosyl}quercetin reduced from 9.2 mg/L to 1.28 mg/L, from 9.2 mg/L to 2.30 mg/L, respectively, after 60 min photooxidation time, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration at 50 W  UV power and at 25°C (Table 3). Patuletin metabolites such as, (E)-ascladiol, (Z)-ascladiol dropped off from 10.3 mg/L to 1.55 mg/L, from 10.3 mg/L to 1.85, respectively, after 60 min photooxidation time, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration at 50 W  UV power and at 25°C (Table 3). Rhamnetin metabolites such as, methyl quercetin, tetrahydroxy-7-methoxyflavone decreased from 7.2 mg/L to 1.15 mg/L, from 7.2 mg/L to 1.44 mg/L, respectively, after 60 min photooxidation time, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration at 50 W  UV power and at 25°C (Table 3). Rhamnazin metabolites such as, Rhamnazin-3-0-β-D-glucopyranosyl-(l →5)- α-L-arabinofuranoside, Rhamnazin-3-O-β-D- glucopyranosyl-(l—»5)-[β-D-apiofuranosyl-(-1→2)]-α -L-arabinofuranoside reduced from 6.5 mg/L to 1.42 mg/L, from 6.5 mg/L to 1.66 mg/L, respectively, after 60 min photooxidation time, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration at 50 W  UV power and at 25°C (Table 3).

Table 3. The metabolites of flavonols in the TW.

2-methoxy-5-methylaniline metabolite such as, 5-nitro-o-toluidine decreased from 134.6 mg/L to 36.34, after 60 min photooxidation time, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration at 50 W  UV power and at 25°C (Table 4). 2,4-diaminoanisole such as, 4-acetylamino-2-aminoanisole, 2,4-diacetylaminoanisole reduced from 275.8 mg/L to 22.06 mg/L, from 275.8 mg/L to 38.61 mg/L, respectively, after 60 min photooxidation time, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration at 50 W  UV power and at 25°C (Table 4). 4,40-diamino diphenyl ether metabolites such as, N,NI-diacetyl-4,4I-diaminobenzhydrol, N,NI-diacetyl-4,4 I –diaminophenylmethane dropped off from 156 mg/L to 28.08 mg/L, from 156 mg/L to 40.56 mg/L, respectively, after 60 min photooxidation time, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration at 50 W  UV power and at 25°C (Table 4). o-aminoazotoluene metabolites such as, hydroxy-OAT (I), 4′-hydroxy-OAAT,  2′-hydroxymethyl-3-methyl-4-aminoazobenzene, 4, 4′-bis(otolylazo)-2, 2′ -dimethylazoxybenzene decreased from 293.6 mg/L to 58.72 mg/L, from 293.6 mg/L to 79.27 mg/L, from 293.6 mg/L to 85.14 mg/L, from 293.6 mg/L to 117.44 mg/L, respectively, after 60 min photooxidation time, at pH=8.0, at 30 mg/L La-ZnO nanocomposite concentration at 50 W  UV power and at 25°C (Table 4). 4-aminoazobenzol metabolites such as phenylhydroxylamine, nitrosobenzol reduced from 178 mg/L to 39.16 mg/L, from 178 mg/L to 44.5 mg/L, respectively, after 60 min photooxidation time, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration at 50 W  UV power and at 25°C (Table 4).

Table 4. The metabolites of polyaromatic amines in the TW.

[34] researched the photocatalytic activity of pure and Ni⁺²-doped BiO samples for the degradation of Rhodamine B (RhB). The effect of Ni⁺² doping concentration on the photocatalytic activity of RhB wasalso investigated. 9 g/L Ni⁺²-doped BiO with a mass ratio of 2wt% had high photocatalytic efficiency [34]. 4-nitrophenol degradation was studied in the presence of Ni doped BiO nanoparticles with a Ni mass ratio of 4% [35]. 78.26% 4-nitrophenol removal was observed the aforementioned nanocomposite after 195 min photodegradation time and at 30 W  UV light irradiation at pH=8 [35]. 68.57% Acid Yellow 29 55% Coomassie Brilliant Blue G250 and 37.27% Acid Green 25 degradations was obtained after 120 min of irradiation in the presence of 0.9% Ni-doped BiO, at 500 W UV light irradiation, under atmospheric oxygen, at 25°C, respectively [36]. The color and pollutant yields obtained in our study exhibited higher yields compared to the studies given above with low Ni-BiO nanocomposite concentrations.

Effect of increasing Ni mass ratios on 30 mg/L Ni doped BiO nanocomposite for photodegradation of TW pollutants

Were researched the effects of different La mass ratios (0.5wt%, 1wt%, 1.5wt% and 2wt% ) in 30 mg/L Ni-BiO nanocomposite concentrations on the photooxidation yields of all pollutants in the TW during photooxidation experiments. Maximum COD_total, COD_inert, total flavonols, TAAs and color removal efficiencies were 99%, 92%, 91%, 98% and 99%, respectively, after 60 min photooxidation time, at pH=8.0, at 1.5wt% Ni mass ratio and at 25°C (Table 5 and Figure 7). Removal efficiencies increased as the Ni mass ratio in the Ni doped BiO nanocomposite were increased from 0.5wt% to 1wt% and to 1.5wt%. Maximum removal efficiencies was measured at 1.5wt% Ni mass ratio in the nanocomposite. The photocatalytic degradation efficiency of BiO nanoparticles increases with an increase in the Ni loading and shows a maximum activity at 1.5 wt%. Then decreases in photooxidation yield was observed on further Ni doping (to 2 wt%). The reason of this can be explained as follows: excessive amounts of dopants can retard the photocatalysis process, because excess amount of dopants deposited on the surface of BiO increases the recombination rate of free electrons and energized holes, thus inhibiting the photodegradation process. Hence, further increase in Ni doping to 2wt% results in the decrease of photocatalytic degradation efficiency.

Table 5. Effect of increasing Ni mass ratios on the TW during photooxidation process after 60 min, at 50 W UV irradiation, 30 mg/L Ni-BiO nanocomposite concentrations, at pH=8.0, at 25°C.

Figure 7. Removal efficiencies of COD_total, COD_inert, total flavonols and TAAs at 0.5wt%, 1wt%, 1.5wt%, and 2 wt% Ni mass ratio.

The synthesized Ni-doped BiO catalyst possesses smaller particle size distribution than pure BiO nanoparticles. Apart from their small size, as Ni⁺² was doped in BiO, more surface defects are produced as reported by [37]. Consequently, the migration of the photo-induced electrons and holes toward surface defects is reasonable [37]. Thus, the separation efficiency of the electron–hole pairs of Ni-doped BiO with more oxygen defects should be more than that of the pure BiO nanoparticles. Therefore, the enhancement in the photocatalytic degradation efficiency of Ni doping BiO increases due to small particle size and higher defect concentration compared to BiO alone.

UV absorbances of Ni-doped BiO

The UV–vis absorption spectra of BiO and Ni-doped BiO are shown in Figure 8. It can be clearly seen from Figure 8. The maximum absorbance shifts is 410 nm for pure nano BiO while the maximum absorbance of Ni-doped BiO with a Ni mass ratio 0.5wt% is observed at a wavelentgh of 380 nm. The wave of absorbance of Ni-doped BiO also increases gradually with increasing the Ni loading and is much higher as compared to that of pure BiO. This could be mainly attributed to the quantum size effect as well as the strong interaction between the surface oxides of Bi and Ni. These observations strongly suggest that the Ni doping significantly affects the absorbance properties.

Figure 8. UV-vis absorption spectra of Ni doped BiO catalysts

The strong UV band gap emission (375–395 nm) results from the radiative recombination of an excited electron in the conduction band with the valence band hole. The broad visible or deep-trap state emissions (410–440 nm and 540–580 nm) are commonly defined as the recombination of the electron-hole pair from localized states with energy levels deep in the band gap, resulting in lower energy emission. These deep-trap emissions indicate the presence of defects or oxygen vacancies of BiO nanostructures [38]. Since the band gap excitation of electrons in BiO or Ni-doped BiO with 254 nm can promote electrons to the conduction band with high kinetic energy, they can reach the solid-liquid interface easily, suppressing electron–hole recombination in comparison with 365 nm. Hence, the observation of low rate at 254 nm is therefore unexpected [39]. The UV band gap emission of Ni-doped BiO nanostructures was increased between 380 and 410 nm after the photocatalytic process of pollutant parameters. The results show that 1.5 wt% Ni-doped BiO has maximum activity as compared to other photocatalysts.

Effect of increasing photooxidation time on the photooxidation yields of pollutants in the TW

Six different photooxidation times (5 min, 15 min, 30 min, 60 min, 80 min and 100 min) was examined during photocatalytic oxidation of the pollutants in the TW. To determine the optimum time for maximum removals these pollutant parameters in the TW. The maximum photocatalytic oxidation removals was observed at 60 min photooxidation time, at pH=8.0 using 30 mg/L Ni doped BiO with a La mass ratio of 1.5wt% at an UV power of 50 W (Figure 9). The removals of COD_total, COD_inert, total flavonols, total aromatic amines and color were found to increase linearly with increase in retention time from 5 min up to 80 min. A further increase in retention time to and 100 min lead to a decrease in yields of pollutant parameters. In other words the removal efficiencies of pollutant parameters (COD components, flavonols, polyaromatics, color) decreased for photooxidation time > 60 min since at long irradiation times since the surface energy of Ni doped – BiO decreases [40]. The photooxidation can form small molecules such as H₂O, carbonmonoxide (CO), CO₂ and benzene etc. after long irradiation; it will lead to the decrease of the polar groups and the oxygen content of pollutant surface. The dispersive component of surface energy, the density of polymer surface has great influence on dispersivity of pollutants in the TW. However, the rate of photodegradation of Ni doped-BiO blends increases with the increase of irradiation time, and is higher than that of photocrosslinking after long irradiation time, leading to the decrease of the density of the polymer surface and the dispersivity of COD, dyes and other pollutants to Ni doped–BiO [41]. The photooxidation can form small molecules such as H₂O, CO, CO₂ and benzene etc. after long irradiation; it will lead to the decrease of the polar groups and the oxygen content of polymer surface, therefore the dispersivity decreaeses resulting in low photooxidation yields [41]. Aromatic and phenolic metabolites which would adsorb strongly onto titania surface and block significant part of photoreactive sites.

Figure 9. Removal efficiencies of COD_total, COD_inert total flavonols and TAAs after 5, 15, 30, 60, 80 and 100 min retention times.

The maximum COD_total, COD_inert, total flavonols, total aromatic amines and color removal efficiencies were 99%, 92%, 91%, 98% and 99%, respectively, after 60 min photooxidation time, at 1.5 wt% Ni mass ratio in 30 mg/L Ni-BiO nanocomposite concentration, at pH=8.0 and at 25°C under 50 W irradiation (Table 6). Also, flavonols such as kaempferol, quercetin, patuletin, rhamnetin, rhamnazin removal efficiencies were 87%, 88%, 90%, 87% and 85%, respectively (Table 6). The photooxidation removals of polyaromatic amines such as, 2-methoxy-5-methylaniline, 2.4-diaminoanisole, 4.40-diamino diphenyl ether, o-aminoazotoluene, 4-aminoazobenzol were 93%, 95%, 87%, 84% and 82%, respectively, after 60 min at pH=8.0 and at 25°C (Table 6). Kaempferol, quercetin, patuletin, rhamnetin, rhamnazin concentrations decreased from 5.7 to 0.741 mg/L, from 9.2 to 1.104 mg/L, from 10.3 to 1.03 mg/L, from 7.2 to 0.936 mg/L, from 6.15 to 0.923 mg/L, respectively. 2-methoxy-5-methylaniline, 2.4-diaminoanisole, 4.40-diamino diphenyl ether, o-aminoazotoluene, 4-aminoazobenzol concentrations decreased from 134.6 to 9.422 mg/L, from 275.8 to 13.79 mg/L, from 156 to 5.46 mg/L, from 293.6 to 10.28, from 178 to 6.23 mg/L, respectively.

Table 6. Effect of increasing photooxidation time on the TW during photooxidation process, at 50 W UV irradiation, at pH=8.0, 30 mg/L Ni-BiO nanocomposite concentrations, 1.5 wt% Ni mass ratio, at 25°C.

The color yields obtained in this study for TW are higher than the studies given below: [42] investigated the effects of Bi0.95Ni0.05O and Bi0.90Ni0.10O on the treatment of Methylene Blue (MB) dyestuff removal under 18 UV irradiation for 1 h. 81% color yields were observed for the aforementioned Ni-Bi-O nanocomposites, respectively [42]. [43] found 80% color yields based on Reactive Black 5 after 60 min irradiation time under 90 W irradiation using Bi-Ni nanocomposite.

Effect of increasing UV powers on the yields of pollutants in the TW

In this study, four UV light powers were used (10 W, 30 W, 50 W and 100 W) to detect the optimum UV irradiation power for maximum photo-removal of the pollutant parameters in the TW using 30 mg/L Ni doped BiO nanocomposite with a Ni mass ratio of 1,5%w. The maximum photocatalytic oxidation removals was observed at 50 W  UV light irradiation, at pH=8.0, after 30 min photooxidation time and at 25°C (Table 7 and Figure 10). The COD_total, COD_inert total flavonols, total aromatic amines and color were found to increase linearly with increase in UV light irradiation from 10 W, up to 30 W, up to 50 W, respectively (Table 7 and Figure 10). Further increase of UV power up to 100 W did not affect positively the pollutant yields. Maximum COD_total, COD_inert, total flavonols, TAAs and color removal efficiencies after photooxidation process were 99%, 92%, 91%, 98% and 99%, respectively, for the aforementioned operational conditions (Figure 10). Flavonols such as kaempferol, quercetin, patuletin, rhamnetin, rhamnazin removal efficiencies were 87%, 88%, 90%, 87% and 85%, respectively, after 60 min photooxidation time, at 50 W  UV light, at pH=8.0, at 30 mg/L Ni-BiO nanocomposite concentration and at 25°C (Table 7). Polyaromatic amines such as, 2-methoxy-5-methylaniline, 2, 4-diaminoanisole, 4, 40-diamino diphenyl ether, o-aminoazotoluene, 4-aminoazobenzol removal efficiencies after photooxidation process were 93%, 95%, 87%, 84% and 82%, respectively (Table 7).

Table 7. Effect of increasing UV light irradiations on the TW during photooxidation process after 60 min, at 30 mg/L Ni-BiO photocatalyst concentration, at pH=8.0, at 25°C.

Figure 10. Removal efficiencies of COD_total, COD_inert, total flavonols and TAAs at 10 W, 30 W, 50 W and at 100 W.

The UV power determines the extent of light absorption by the semiconductor catalyst at a given wavelength. During initiation of photocatalysis, electron–hole formation in the photochemical reaction is strongly dependent on the optimum light intensity [44]. In this study, as the UV power increase from 10 W up to 50 W might favor a high-level surface defects, which account for the increase in the defect emission relative to the UV emission as reported by [39]. Higher UV powers > 50 W decrease the defects in the surface of the nanoparticle by disturbing the active holes.

Effect of increasing pH values on the pollutant yields in the TW

The effects of increasing pH values (4.0, 6.0, 8.0 and 10.0) on the photocatalytic oxidation of polutant parameters in TW was examined by considering the solubility of BiO nanoparticles in acidic as well as in highly basic solutions. The maximum photocatalytic oxidation removals was obtained at pH=8.0, after 60 min photooxidation time with a Ni mass ratio 1.5wt% using 30 mg/L Ni-BiO nanocomposite concentration at 50 W  UV power (Table 8 and Figure 11). In acidic medium, less photocatalytic degradation of pollutant parameters (COD components, flavonols, polyaromatics, color) was observed. The extent of photocatalytic degradation of polutant parameters was found to increase with increase in initial pH to 8.0 and a decrease in maximum photocatalytic degradation was found at pH 10. The possible explanation of this is that the pH at zero point charge (zpc) of BiO is 9.0 ± 0.3 [45]. Below pH 8.0, active sites on the positively charged catalyst surface are preferentially covered by pollutant molecules. Thus, surface concentration of the polutant parameters (COD components, flavonols, polyaromatics, color) is relatively high, while those of OH^– and OH^● are low. Hence, photocatalytic degradation decreases at acidic pH. On the other hand, above pH 8.0, catalyst surface is negatively charged by means of metal-bound OH^–, consequently the surface concentration of the polutant parameters (COD components, flavonols, polyaromatics, color) is low, and OH^● is high. In addition, polutant parameters are not protonated above pH 8.0. The electrostatic repulsion between the surface charges and Ni doped BiO nanocomposite hinders the amount of polutant parameters and the adsorption, consequently surface concentration of the polutant parameters decreases, which results in the decrease of photocatalytic degradation at pH 10.0. In conclusion, pH 8.0 can provide moderate surface concentration of polutant parameters which react with the holes to form OH^●.

Table 8. Effect of increasing pH values on the TW during photooxidation process, at 50 W UV irradiation, after 60 min, at 25°C.

Figure 11. Removal efficiencies of COD_total, COD_inert, total flavonols and TAAs at pH=4.0, pH=6.0, pH=8.0, pH=10.0.

Photocatalytic oxidation mechanisms of Ni doped BiOnanocomposite

The higher activity of Ni doped BiO can beattributed to successful e⁻–h⁺ separation and production of ●O₂⁻ and OH^●. Ni-modified BiO sample manifests the highest efficiency, which may be explained by the highest number of O₂ vacancies (related to the different charge and electronegativity of Ni and Bi ions) and as a result of stronger adsorption of OH⁻ions onto the BiO surface [46]. This favors the formation of OH^● by reaction of hole and OH⁻. The OH^● and photogenerated ●O₂⁻has extremely strong non-selective oxidants lead to the degradation of the organic pollutant at the surface of Ni modified BiO [41]. The photocatalytic degradation mechanism starts with the illumination of BiO nanoparticles and production of electron–hole pairs in Eq. (2):

Major roles of metal ions in this study are to increase the concentration of BiO on the surface of the catalyst and to prolong the individual life-time of electrons and holes and hence, inhibit their recombination. The ability of Ni⁺³ to scavenge photogenerated electrons is as follows: (Eq. 3):

However, stabilities of Ni⁺³ ions may be disturbed in their reduced forms (Ni⁺²). This can be achieved by transferring the trapped electron to O₂ [Eq. (4)]:

The produced O₂⁻● is responsible from the generation of OH^●, known as highly reactive electrophilic oxidants [Eqs. (5-7)]:

In the meantime, photogenerated holes may react with H₂O molecules and produce OH^● (Eq. 8):

The color removal by photooxidation of dyes reactions were given in Eqs (9-14):

Thus, loading of metal ions such as Ni on the surface of BiO matrix can suppress the recombination of photoinduced charge carriers either with only electron capture ability or with steps forward to produce OH^●. For Ni–BiO, electron accepting ability, production of more OH^●, the highest surface roughness value and the higher dark adsorption capacity result in pronounced photoactivity. The decay profile of the products includes the subsequent attacks of OH^●, known as highly reactive electrophilic oxidants. The main reaction pathway (60% of OH^●) is the addition of the OH^● to the double bond of the azo group, resulting in the rapid disappearance of color; however, addition to the aromatic ring also occurs (40% of OH^●) [47, 48]. Further OH^● attacks and the increment in OH^● concentration in the solution increase the yield of OH^–adduct in the degradation progress of each product. The opening of the dye aromatic rings due to consecutive oxidation reactions leads to low-molecular weight compounds [49].

Photonic efficiency of Ni doped BiO

In order to evaluate the relative photonic efficiency (Ir), a solution of MCP (40 mg/L) adjusted to pH 10 was irradiated with 100 mg BiO (Merck) and Ni-doped BiO, separately. The relative photonic efficiencies of light of wavelengths 254 and 365 nm for BiO and Ni-doped BiO are presented in Table 9. For comparison, the relative photonic efficiency of TiO₂ is also presented in Table 9. The relative photonic efficiencies of Ni-doped BiO are greater as compared to those of BiO and TiO₂, revealing the effectiveness of metal-doped systems. It is also interesting to note that the relative photonic efficiency for Ni-doped BiO for light of wavelength 254 nm are much higher as compared to that for 365 nm. The results are in good agreement with degradation and mineralization studies. Comparing the high efficiency of Ni doped BiO catalysts with standard BiO and TiO₂ catalyst, the photocatalytic efficiency of 1.5 wt% Ni-doped BiO is higher as compared to that of BiO and TiO₂ and other Ni doped BiO nanacomposites.

Table 9. Comparison of relative photonic efficiencies in the photodegradation of pollutants in TW by BiO and Ni-doped BiO photocatalysts (*)

Reusability of Ni doped BiO

As shown in Figure 12, after the first cycle of photocatalytic oxidation within 60 min, 99% of the Ni doped BiO with a mass ratio of 1.5wt% was recovered. After three cycles, the phoooxidation ability of Ni doped BiO nanocomposite was retained at 93% of the original value. After 8th cycles the nanocomposite was reatined at 80%. One of the reasons for the slight decline in photooxidation is that the surface of the reused photocatalysts may exist with some low residual substances which did not occupy the photocatalytic sites and did not block the adsorption. The presence of Ni significantly changed the binding site of the pollutant molecules. It is possible that the oxygen atom in Ni-BiO was bound to the dopant Ni [50]. The speedily recovering of the photodegradation capacity of Ni doped BiO for pollutans photodegradation will benefit to their photocatalytic activity.

Figure 12. The reusability of Ni doped BiO

Conclusions

By using 30 mg/L Ni-BiO with a Ni mass ratio of 1.5w% the COD_total, COD_inert, flavonols, polyaromatics and color were photodegraded with yields as high as 82-99% within 60 min photooxidation time, at 25°C under 50 W  UV power, at pH=8.0. The addition of Ni to BiO lead to enhance the photocatalytic activity by increasing the total surface area. The flavonoids and polyaromatic amines and their metabolites in the TW were firstly determined photodegraded with high rates and photonic efficiency using 30 mg/L Ni-BiO with a Ni mass ratio of 1.5w% at pH 8.

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