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Pharmaceutical wastes can result from many activities and locations in a healthcare facility. Anywhere medicines are employed can be the site of spills, half-used bottles, equipment with residual medicine on it. Prescription and over-the-counter drugs end up as pharmaceutical waste as do instruments like gloves, masks and bottles. The source of pharmaceuticals in water is not just from manufacturing plants but also from the antibiotics and drugs which are used in the livestock industry. Some examples of these compounds are Carbamazepine, Sulfamethoxazole, Triclosan and Diclofenac. High consumption patterns of Pharmaceutical Compounds associated with their high chemical stability and low biodegradability, contributed to their widespread release in the aquatic environment. This led to a major threat firstly to aquatic life and consequently to the whole food chain. Pharmaceuticals encompass a huge range of chemical compounds and they have all sorts of different effects on humans and plants too.Current methods include UV disinfection, ozone or chloride, and advanced water treatment technologies(which includes activated carbons adsorption, membrane filtration, advanced oxidation processes (AOPs)).Bismuth-based semiconductors( eg: Bi2O3,Bi2S3) are a unique and promising group of recently developed advanced photocatalytic materials. They have been widely applied in several areas including decomposition of organic and inorganic pollutants in wastewater, and organic synthesis through harvesting the energy of light. The electronic structure of bismuth-based semiconductors confers them with a suitable band gap for visible-light response and a well-dispersed valence band making them a promising candidate when compared to other semiconductors.

Review of Bismuth Based Photocatalysts for Degradation of Pharmaceuticals Waste in Wastewater.

PhCs are a very large group of living micropollutants of emerging anxiety. Corrective studies therefore tend to focus on a small group of PhCs who are classified as repeaters in general water treatment technology and representatives of different classes of medical and chemical applications. Following the three selected PhCs considered in this review: carbamazepine (CBZ) antiepileptic, diclofenac (DCF) anti-inflammatory and analgesic, and sulfamethoxazole (SMX) antibiotic.

Pharmaceutical Compounds as Pollutants of Emergent Concern

PhCs are important in ensuring high levels of human health and well-being and are widely used in animals, being the most widely available chemicals in modern societies. However, it has been proven that high-performance PhC patterns coupled with their high chemical resistance and low biodegradability, have contributed to their widespread emissions in the aquatic environment (especially those that are highly soluble). With the provision of biological function and repetitive behavior of several PhCs, they form the first major treatment in aquatic life and as a result throughout the food chain. Aside from public health concerns regarding the short- and long-term toxic effects associated with exposure to high-volume PhCs for drinking water and food chains, the environmental perspective of the problem has come with a relevant topic

CBZ, DCF, and SMX Detections in Wastewater and Environmental Water

Since the first surveillance studies in the 1980s and 1990s CBZ, DCF, and SMX have been detected in wastewater and natural water samples in the ng / L-μg / L range. Between 1996 and 2000 Heberer monitored 24 PhCs in sewage treatment plants (STPs) and natural water from the Berlin urban area and CBZ, DCF, and SMX were compounds found at higher altitudes. The results were allowed to conclude that only 8% CBZ and only 17% DCF were released during wastewater treatment. As a result, it is not surprising that fractions of up to 1.1 μg / L CBZ and 0.6 μg / L DCF were found in the surface water of the Berlin city. In 2001, Ternes reported the removal of meaningless CBZ from municipal STP, DCF treatment was effective (69%). CBZ and DCF were also found to be at the same level of exposure to STP contaminated water as well as natural water from other European and Brazilian countries. First monitoring studies also report SMX detection in water STPs at 00.9 μg / L but up to 2.0 μg / L

Photodegradation

As mentioned earlier, the occurrence of CBZ, DCF, and SMX in natural waters around the world is due to the low performance of conventional water treatment methods as barriers for these PhCs, due to their high chemical stability and low biodegradability. Once they are in nature, the future of these PhCs in the water cycle depends on their properties namely their hydrophobic / hydrophilic properties which will determine their contact with water, dissolved solids, and durability, and their stability under sunlight.

Photodegradation at a high level of surface water can be a natural elimination method for resistant PhCs in natural waters. Direct and indirect photochemical processes can occur depending on the nature of the PhC, water matrix, and spectral irradiance spectrum. Direct photolysis of the organic compound occurs only when the absorption spectrum comprises the magnitude of the incoming irradiation, leading to the electronic enjoyment of the molecule that promotes its phototransformation conversion. In indirect processes, photoactive compounds - photosensitizers - absorb sunlight that produce active compounds such as hydroxyl radicals (OH ●) that can cause a decrease in PhCs. According to the UV spectra it may be concluded that very small particles of sunlight (i.e., UV-A and UV-B) are expected to promote direct photolysis of CBZ, DCF, and SMX.

Photocatalysis

In 1972, Fujishima and Honda discovered a photoelectrocatalytic water separation using a TiO2 electrode and paved the way for efficient use of light in chemical processes. Since then photocatalysis has grown rapidly in many areas of environmental use and energy, it is considered the solution to global energy shortages and the fight against environmental degradation. According to Fujishima and his colleagues, over a decade the basic scientific knowledge in TiO2 photocatalysis has allowed the development of a technological field that reaches real industrial exploitation, so it is an excellent example of science solving real word challenges.

Effective use of solar spectrum of active photodegradation of persistent PhCs as in the case of CBZ, DCF, and SMX can be achieved by using materials with photocatalytic properties, as is the case with semiconductors. As the aforementioned TiO2 is the most popular photocatalyst due to its unique properties: penetration, high performance and image performance, cost savings and non-toxicity to humans and the environment. Other iron oxides (e.g., ZnO, WO3), and their products have also been tested for organic chemical degradation. In addition to the classical metal oxide semiconductors, the pioneering work of Wang et al. in 2009 the emergence of H2 with graphite carbon nitride stainless steel (g-C3N4) was observed under visible light, thereby elevating the first stainless photocatalyst. Since then these solids-g-C3N4 and derivatives, as well as other polymers act as polyaniline (PANI), polyacetylene, polythiophene, polypyrrole, poly-p- ( phenylenevinylene) - guaranteed to promise portable photocatalysts of light for several important reactions (eg photochemical water separation, oxidation reaction, CO2 reduction, pollution and disinfection), and play an important role in the transformation of biomass, i.e., continuous chemical processes.

Due to its wide range of properties, dark body structures, and highly conducive mobility, carbon materials have been extensively studied such as drugs, composites or semiconductors accessories. Undoubtedly, they are the most effective way to improve photocatalytic activity, as evidenced by the number of book studies reviewing TiO2 / carbon performance over the past decade. Example Khalid et al. compared with the performance of TiO2 / carbon nanomaterials against empty TiO2 concludes that carbon doping and compounds containing active carbon, fullerene, carbon nanotubes (CNTs), or graphene leads to substances with improved photocatalytic activity , adsorption power, electron degradation ability and stimulus, visual enhancement of light absorption, and easy separation also. Improved photocatalytic activity due to the addition of carbon to a semiconductor can be considered by looking at two methods (i) advanced charge separation in the presence of carbon, (ii) carbon acting as a photosensitizer. When porous carbons are added to semiconductors, the many effects of interaction due to advertising should be considered. The method of separating coins produced by semiconductor / carbon composites was proposed by Woan et al. He assumes that carbon-containing materials have the ability to trap electrons produced in a semiconductor, thus preventing reconnection. Wang et al. proposed a method in which carbon is used as photosensitized by transmitting electrons to the semiconductor conduction group.

Semiconductor

Doping semiconductors is a method of enhancing their physical properties from the inclusion of metal or atoms that cannot be matched with other materials, or the addition of atoms in certain positions, by maintaining a crystalline semiconductor structure, can alter the onset of UV response in the visible region. Several metals (e.g., W, V, Fe or Cu) and illegal metals (B, C, N, F, P, S, Cl, and Br) have been used to successfully extract TiO2. Among nonmetals, N- and C-doping are similar in that they both favor the formation of oxygen gaps, enhancing the photocatalytic activity of TiO2 in the visual region. Theoretical study by Valentin et al. reveals that in low C concentrations C-doped TiO2 features depend on O availability during the fusion: O-C inputs and O spaces are preferred under adverse O2 conditions, whereas interstitial C and Ti-ins with C atoms is preferred in O2-rich cases.

Semiconductor/Activated Carbon

As mentioned, the use of semiconductors has several drawbacks related to integration, high repetition of e-h / h + pairs built up, limited function under sun and day separation. To overcome these problems the scientific community explores different strategies. Back in early 1989, Tanguay et al. reported that carbon-based anatase TiO2 was found to be effective in reducing dichloromethane degradation, and allowed easy separation of catalyst in the reaction component. Between 1998 and 2001, Matos et al. reported that the addition of amorphous carbon phase (e.g., activated carbon) to a semiconductor in a mixed suspension improves photo actor performance for biological pollutants. Reduction of semiconductor photocatalysts in solid solids is a way to improve their performance, and among many experiments, active carbons meet the requirements requested to be considered essential services because (i) allow for strong adhesion between catalyst and support, (ii) catalyst recycling is not affected by the attachment process, (iii) has a high surface area, and (iv) has a high adsorption relationship with respect to contaminants.

In fact, several studies suggest that the use of active carbon as a support material can increase the degree of termination by continuously allowing an increasing amount of substrate to interact with weak metal oxide through adsorption, by reducing e - / h + oxide reuptake of iron, and due to the dark nature of the activated carbon harvesting the solar spectrum is popular. Studies aimed at examining the synergetic effects of semiconductor / carbon nanocomposites have shown that increased exposure to contaminants in the carbon phase used, closely followed by interphase transfer in the TiO2 phase, provides a complete photodegradation process. In 2011, Lim et al. reviewed the synergistic adsorption-photocatalytic processes of TiO2 / active carbon compounds that address the challenges and ongoing advances in water treatment and rehabilitation. The authors propose a combination of these compounds with membrane separation technology to obtain and rejuvenate compounds and improve solar harvesting using N-doped carbons. Improvements in solar spectrum harvesting and energy efficiency techniques have also been identified by Chong et al. as an urgent need to provide affordable photocatalytic technology in the field of water treatment. As mentioned, the use of semiconductors has several drawbacks related to integration, high repetition of e-h / h + pairs built up, limited function under sun and day separation. To overcome these problems the scientific community explores different strategies. Back in early 1989, Tanguay et al. reported that carbon-based anatase TiO2 was found to be effective in reducing dichloromethane degradation, and allowed easy separation of catalyst in the reaction component. Between 1998 and 2001, Matos et al. reported that the addition of amorphous carbon phase (e.g., activated carbon) to a semiconductor in a mixed suspension improves photo actor performance for biological pollutants. Reduction of semiconductor photocatalysts in solid solids is a way to improve their performance, and among many experiments, active carbons meet the requirements requested to be considered essential services because (i) allow for strong adhesion between catalyst and support, (ii) catalyst recycling is not affected by the attachment process, (iii) has a high surface area, and (iv) has a high adsorption relationship with respect to contaminants. In fact, several studies suggest that the use of active carbon as a support material can increase the degree of termination by continuously allowing an increasing amount of substrate to interact with weak metal oxide through adsorption, by reducing e - / h + oxide reuptake of iron, and due to the dark nature of the activated carbon harvesting the solar spectrum is popular. Studies aimed at examining the synergetic effects of semiconductor / carbon nanocomposites have shown that increased exposure to contaminants in the carbon phase used, closely followed by interphase transfer in the TiO2 phase, provides a complete photodegradation process. In 2011, Lim et al. reviewed the synergistic adsorption-photocatalytic processes of TiO2 / active carbon compounds that address the challenges and ongoing advances in water treatment and rehabilitation. The authors propose a combination of these compounds with membrane separation technology to obtain and rejuvenate compounds and improve solar harvesting using N-doped carbons. Improvements in solar spectrum harvesting and energy efficiency techniques have also been identified by Chong et al. as an urgent need to provide affordable photocatalytic technology in the field of water treatment.

Bismuth-Based Photocatalytic Materials

Bismuth trioxide (Bi2O3) is the simplest and most important compound of bismuth. It has potential uses, among other things, in many gases and in ceramic glass solid oxide fuel cells. It has also been used as a photocatalyst for both water separation and decomposition of natural contaminants. Bi2O3 as a semiconductor has a band gap that varies from 2.1 eV to 2.8 eV, making it a bright and portable photocatalyst. Bi2O3 Polymorphs include alpha (monoclinic), beta (tetragonal), gamma (body-focused cubic), delta (facial-focused cubic), and omega (triclinic) categories ). These variable phases can be easily converted to α phase at low temperatures and  at phase at high temperatures. Continuous mutations in (BiO) 2CO3 have also been observed, and this chemical instability indicates a major obstacle to the continued use of Bi2O3 as a photocatalyst. Methods involving metal doping, ion doping, and compounding have been tried, but they still have to overcome this internal problem.

The Bi2S3 has a 1.7 eV bandwidth gap and is ideal for photocatalytic light harvesting due to its high light and near IR performance. Various types of Bi2S3 nanocrystals have been prepared, from 1D nanods and 2D nanosheet to standard oxygen-free and hot injection techniques, to 3D spheres-like spheres in a solvothermal manner. Imertured holes in the Bi2S3 valence belt with a quiet power of 1.62 eV, and the production of hydroxyl radicals (radical dotOH) can be components to eliminate the decay of dye impurities. Photocatalytic reduction of CO2 to methyl formate (MF) in the presence of Bi2S3 has also been reported. Bi2S3 has a small band gap and when combined with other photocatalysts such as TiO2, Bi2WO6 and CdS, the duplicate rate of / h + pairs may decrease which has led to further improvements in the performance of -photocatalytic under visible radiation.

Bi2MO6 (M = Cr, Mo, W) is the simplest member of the Aurivillius family, the standard formula Bi2An-1BnO3n + 3 (A = Ca, Sr, Ba, Pb, Bi, Na, K; B = Ti, Nb , Ta, Mo, W, Fe). Theoretically, the electronic structure of Bi2MO6 can be modeled based on the concept of human density (DFT). The crystal structure of Bi2MO6 falls under the orthorhombic space group Pca2 (1). The results obtained suggested that both the valence band and the bi2MO6 conduction band were composed of hybridized Bi 6p, O 2p and M nd (n = 3, 4, and 5 for Bi2CrO6, Bi2MoO6 and Bi2WO6, respectively) orbitals. Predicted band gaps shown are 1.245 eV, 1.96 eV and 2.2 eV for Bi2CrO6, Bi2MoO6 and Bi2WO6, respectively. These predictions are smaller than the test results, which determine the band spaces to be 2.16 eV, 2.63 eV and 2.77 eV for Bi2CrO6, Bi2MoO6 and Bi2WO6. The discrepancy is due to known limitations of the GGA. However, both suggest that the Bi2MO6 chemicals are suitable for light photocatalysts. It should also be noted that Bi2CrO6, despite having a very small Bi2MO6 gap, is not suitable for photocatalysis due to the re-integration of electrons with the built-in holes. Therefore, few studies have focused on the use of Bi2CrO6 in photocatalysis.

BiVO4

Bismuth vanadate (BiVO4) exhibits interesting natural properties including ferro-elasticity and ionic conductivity. It has recently been introduced in the field of photocatalysis driven by bright light and has a theory gap of 2.047 eV, as calculated by the DFT method. The BiVO4 valence band mainly consists of O 2p and V 3d orbitals. There are three classes of BiVO4, namely monoclinic fergusonite, tetragonal sheelite and tetragonal zircon. The transition of the transverse phase between monoclinic fergusonite and tetragonal sheelite occurs at 255 ° C.

Many ways to make BiVO4 have been reported. Monoclinic BiVO4 has been developed for both solid reaction (SSR) and melting response at high temperatures. Tetragonal BiVO4 is obtained by air conditioning at room temperature. The monoclinic and tetragonal BiVO4 band spaces are 2.4 eV and 2.9 eV, respectively, indicating that the selective preparation of monoclinic BiVO4 has the advantage of making a photocatalyst operated by active light intensity. An additional mechanism for the preparation of monoclinic crystal and tetragonal crystal BiVO4 with a simple aqueous process has also been reported. Recently, the hydrothermal method has also been used successfully in the preparation of the monoclinic BiVO4. The use of the hydrothermal method has several advantages including low test conditions, simple test equipment, and controlled conditions capable of producing BiVO4 structures.

BiVO4 has been widely used in photocatalytic damage of organic contaminants under visible light (e.g., RhB and phenol), and has shown excellent removal efficiency compared to N doped-TiO2. BiVO4 photocatalyst has also been used in water cracks. However, it was found that BiVO4 is an active photocatalyst of O2 evolution under visible light rays, the power of the conduction band may not be high enough to produce H2 with H2O reduction. In a separate study, Liu et al. reported the ability to specifically select ethanol from photocatalytic reduction of CO2 in the presence of BiVO4 under visible light rays. Booshehri et al. also found that BiVO4 is a promising candidate for the use of photocatalytic inactivation of bacteria in water under visible light irradiation.

BiOX (X = F, Cl, Br, I)

Bismuth oxyhalides are as strong as photocatalysts because of their visible properties. The crystal structure of BiOX consists of a layer structure of [Bi2O2] slabs composed of slabs of double halogen atoms. BiOX electrical properties are simulated based on the DFT method. Both the valence band and the biOX conduction band contain X np (n = 2-5 of X = F, Cl, Br and I, respectively), O 2p, and Bi 6p orbitals. The bandits listed scientifically for BiOF, BiOCl, BiOBr and BiOI bands are 2.79 eV, 2.34 eV, 1.99 eV, and 1.38 eV, respectively. By comparison, their band spacing was determined by 3.64 eV, 3.22 eV, 2.64 eV, and 1.77 eV, respectively. The difference between the calculated and test results of the band spaces is due to the existing limitations within the GGA method. However, both show that band spaces are usually reduced by the increasing number of atoms. Only UV light can be used to make BiOF act as a photocatalyst, while both visible light and nearby IR are effective in using BiOI embedded in photocatalysis. As a result, BiOBr and BiOCl are often studied because of their proper belt spaces.

(BiO) 2CO3

Bismuth subcarbonate ((BiO) 2CO3 or Bi2CO5) is the only solid carbonate well established in the Bi2O3-CO2-H2O system. The bandwidth of the (BiO) 2CO3 band is 3.4 eV, and as a result only radiation with a wavelength of less than 365 nm can change the band gap. The steering band of the (BiO) 2CO3 mainly consists of O 2p and Bi 6p orbitals, while the valence band is formed by the orbitals of O 2p, Bi 6p and C 2p. The template-free hydrothermal method was successfully used to prepare (BiO) 2CO3 with empty microspheres, its formation was time-dependent and was followed by Ostwald growth structures. Based on the use of (BiO) 2CO3, this compound demonstrated photocatalytic activity in disinfection and oxidation of pollutants (dye, NO, etc.) in polluted water and polluted air.

Major Challenges and Possible Approaches

Energy Band Engineering Analysis

Semiconductor power band configurations are very important for many photocatalytic structures, such as the length of the excitatory irradiation, the redox capacity of the built-in holes and electrons, and the degree of repetition of electron pairs / holes. The strength of flat-band semiconductors can be calculated using Mulliken electronegativity theory of atoms.

EVB is the high position of the valence band, e.g. gap band value of semiconductor, isp is the semiconductor power choice, and Ee is the free electron power on the hydrogen scale (∼4.5 eV). The electronegativity of a semiconductor, χp, can be measured by the geometric mean of electro negativities of existing atoms. The electro and negativities of all computers are summarized in Table 2. The band positions of the semiconductors were dependent on pH variations of 0.059 V / pH at 25 ° C and 1 atm (Nernstian relationship). Redox power of H + / H2 (0 V vs. NHE) and O2 / H2O (1.23 V vs. NHE). Belt spaces can also be found in electron volts. The minimum wavelength (λmin) radiation that would activate the electron transition from the valence band to the conduction band can be calculated.

It can be concluded that the four compounds (BiOF, BiOCl, BiPO4 and (BiO) 2CO3) do not respond to visible light. Others, such as Bi2WO6 and BiOBr, are less visible - they respond more lightly. Proper use of visible light in the spectrum was increasingly becoming one of the major challenges in the use of bismuth-based semiconductors such as photocatalysts.

An important branch of photocatalysis application is in the water separated to produce H2 and O2. The reaction requires that both semiconductor high valence belts be better than the redox power of O2 / H2O (1.23 V vs. NHE), and that the bottom of the semiconductor conductor belt is worse than the redox H + / H2 (0 V vs NHE). It can be seen that all valence belt positions satisfy these conditions. However, most of the reducing electrons in the conduction bands are too weak to reduce H + to H2. This presents an additional challenge for the use of bismuth-based materials in photocatalytic water separation.

Improvement of  Visual Light Sensitivity

Power Band Fluctuations

In terms of band formation, improving the visual light sensitivity reduces the band gap. Under the operating bands slightly lower or higher than the redox power of H+/H2, while almost all valence band peaks are better than the redox power of O2/H2O. Therefore, flexibility of the valence band to reduce the band gap can be preferred, taking into account the durability of the material. The main methods include using doping with 3d-change materials, with cations with d10 or d10s2 correction, and non-metallic materials.

By combining elements with 3d transformations, it has been reported that the 3d dopants regions insert a new band into the original band space and switch to lower power with an increase in the atomic number of dopants. The power of the contaminant belt can be considered as the top of the valence band, to reduce the gap of the belt and make it easier to detect the visible light energy of a doped semiconductor. It has also been extended to bismuth based photocatalysts modification applications, aimed at improving the sensitivity of visible light. Xu et al. reported that in preparation for Cu-BiVO4, where the dose of tablets varied from 0.5 to 20 to 20%, the band spaces were reduced from 2.40 eV for BiVO4 to 2.31 eV for Cu (20 at% ) - BiVO4. Similarly, the visible functions performed by photocatalytic light were enhanced in natural pollutants. Improved photocatalytic performance by doping Bi2O3 with a 3d-transition device (Ni and Zn) has also been reported by Malathy et al. Band spaces have been changed from 2.8 eV for Bi2O3 to 2.69 eV for Ni-Bi2O3 and 2.74 eV for Zn-Bi2O3. As a result, photocatalytic activity in degradation MG (triphenyl methane dye) was enhanced by 12.5% ​​and 275% under visible light of 180 minutes. It should also be noted that when doping with 3d-transition materials, the sensitivity of the visible light is enhanced by inserting 3d states into the belt gap. However, this pollution can increase the mass of the masses, which can be the regenerative centers of electrons and holes. Also, a complete 3d orbital prevents electron transfer. These two factors may undermine the final photocatalytic activities and should be considered.

Pharmaceuticals like Diclofenac, Sulfamethoxazole and Triclosan are hazardous if dispersed in water bodies, both to the ecosystem and to aquatic life. Hence, they require proper disposal methods. Current methods involve using photocatalysts which get activated only when irradiated with UV radiation, which is not very cost efficient. Bismuth based photocatalysts, on the other hand, solve this concern by getting excited by visible radiation itself and not requiring any extra energy for extraction of UV radiation.

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