Synthesis of magnetically separable Bi2O4/Fe3O4 hybrid nanocomposites with enhanced photocatalytic removal of ibuprofen under visible light irradiation

A Review on the Use of Metal Oxide-Based Nanocomposites for the Remediation of Organics-Contaminated Water via Photocatalysis: Fundamentals, Bibliometric Study and Recent Advances

The improper disposal of toxic and carcinogenic organic substances resulting from the manufacture of dyes, drugs and pesticides can contaminate aquatic environments and potable water resources and cause serious damage to animal and human health and to the ecosystem. In this sense, heterogeneous photocatalysis stand out as one effective and cost-effective water depollution technique. The use of metal oxide nanocomposites (MON), from the mixture of two or more oxides or between these oxides and other functional semiconductor materials, have gained increasing attention from researchers and industrial developers as a potential alternative to produce efficient and environmentally friendly photocatalysts for the remediation of water contamination by organic compounds. Thus, this work presents an updated review of the main advances in the use of metal oxide nanocomposites-based photocatalysts for decontamination of water polluted by these substances. A bibliometric analysis allowed to show the evolution of the importance of this research topic in the literature over the last decade. The results of the study also showed that hierarchical and heterogeneous nanostructures of metal oxides, as well as conducting polymers and carbon materials, currently stand out as the main materials for the synthesis of MON, with better photocatalysis performance in the degradation of dyes, pharmaceuticals and pesticides.

Efficient photocatalytic degradation of emerging ciprofloxacin under visible light irradiation using BiOBr/carbon quantum dot/saponite composite

The use of visible-driven photocatalysts has fascinated attention as a capable and sustainable approach for wastewater remediation. In this work, BiOBr/carbon quantum dot (CQDs)/saponite composites (CQDs/Clay@BiOBr) were fabricated via hydrothermally using two different CQDs/Clay precursors (in-situ synthesis (IS) and physical mixing (PM)). The obtained products were characterized, and the photocatalytic performances of the prepared samples were evaluated in the photocatalytic decomposition of emerging ciprofloxacin (CIP) pharmaceutical waste. The highest CIP mineralization performance was achieved when a combination of BiOBr and CQDs/Clay (IS) with the appropriate proportion because the strong adhesion between CQDs and clay generate a great heterojunction in the composite. The stronger interaction of CQDs and better distribution of CQDs on the surface of clay in the CQDs/Clay (IS) enhanced the interaction of BiOBr and CQDs, and avoided the re-agglomeration of excess of CQDs on surface of BiOBr which reduce the active surface to receive the light and react with CIP. The ultrafast degradation rate of the optimized CQDs/Clay@BiOBr composite was better compared to others. The significant improvement in the CIP degradation efficiency of the CQDs/Clay@BiOBr composite was attributed to the excellent separation and transportation of photogenerated electrons and holes, as confirmed by photoluminescence, photocurrent density, and electrochemical impedance spectroscopy results. Moreover, the photocatalytic degradation mechanism of CIP in the CQDs/Clay@BiOBr composite was proposed based on the electronic states of each material in the composite and on a scavenger test. Thus, the proposed CQDs/Clay@BiOBr composite can be employed as a potential visible-light-driven photocatalyst for the decomposition of organic contaminants in wastewater.

Removal of ibuprofen from synthetic wastewater using photocatalytic method in the presence of FeO photocatalyst supported on modified Iranian clinoptilolite

This study investigated the removal of an organic drug called ibuprofen from the wastewater containing this drug. Iron oxide supported on modified Iranian clinoptilolite was used as the photocatalyst in the presence of the light of a solar lamp. XRD, SEM, EDAX, and FT-IR analyses were performed to detect the prepared photocatalyst. The results of photocatalytic identification analyses proved the suitable loading of iron oxide supported on modified Iranian clinoptilolite. This study investigated the effect of initial concentration of ibuprofen (5-25 mg/L), photocatalyst concentration (100-300 mg/L), and process time (10-240 min) on the removal from ibuprofen from wastewater containing this drug. The experiments were performed in a setup in the presence of a solar lamp with a flux of 300 W/m². The results indicated that with the initial ibuprofen concentration of 25 mg/L, photocatalyst concentration of 300 mg/L, and time of 210 min, the highest percentage of ibuprofen removal and ibuprofen adsorbed on the catalyst were 99.80% and 83.17 mg/g, respectively. Kinetic modeling was then performed using the Langmuir-Hinshelwood model, and a quasi-first-order kinetic model showed a good agreement with the results obtained. Finally, the recovery of the photocatalyst was investigated, and the results showed that under optimal conditions about 91% of ibuprofen was removed after five re-uses of the photocatalyst.

Carbon quantum dots sensitized 2D/2D carbon nitride nanosheets/bismuth tungstate for visible light photocatalytic degradation norfloxacin

A novel carbon quantum dots (CQDs) sensitized 2D/2D carbon nitride nanosheets and bismuth tungstate composite (CQD-CNs/BWO) was successfully prepared via the facile hydrothermal method and used for the photocatalytic degradation of norfloxacin (NOR). During 120 min irradiation test, CQD-CNs/BWO exhibited 9 and 1.76 times higher photocatalytic activity than CNs and BWO, respectively. CQDs and constructed 2D/2D structure could not only improve the light harvesting but also promote the generation and separation of electron-holes. The existing inorganic ions in solution (e.g. bicarbonate ions, chlorine ions, and sulfate ions) could inhibit NOR degradation. Based on the electron spin resonance and free radicals inhibition tests, the holes and superoxide radicals rather than hydroxyl radicals were the main reactive species. The intermediates and possible pathways were proposed, and the antibacterial activity of the treated solution after the reaction was evaluated via bacteriostatic tests. The prepared composite material with high photocatalytic activity and stability is potentially effective for the degradation of antibiotics in wastewater.

Functioned catalysts with magnetic core applied in ibuprofen degradation

In the present work, the performance of Ag/ZnO/CoFe₂O₄ magnetic photocatalysts in the photocatalytic degradation of ibuprofen (IBP) was evaluated. This study considered the use of pure Ag/ZnO (5% Ag) and also the use of the Ag/ZnO/CoFe₂O₄ magnetic catalysts containing different amounts (5, 10 and 15% wt) of cobalt ferrite (CoFe₂O₄). The catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoacoustic spectroscopy. To carry out the photocatalytic degradation reaction, different concentrations of the ibuprofen contaminant solution (10, 20 and 30 ppm) and different concentrations of photocatalyst were tested (0.3 g L^-1, 0.5 g L^-1 and 1.0 g L^-1). The reaction parameters studied were: IBP concentration, catalyst concentration, adsorption and photolysis, influence of the matrix, radiation source (solar and artificial) and the effect of organic additive. At the end of the photocatalytic tests, the best operating conditions were defined. Considering the obtained results of degradation efficiency and magnetic separation, the optimal parameters selected to proceed with the other tests of the study were: ibuprofen solution concentration 10 ppm, Ag/ZnO/CoFe₂O₄ (5%) catalyst at a concentration of 0.3 g L^-1 and pH 4.5 of the reaction medium. The results indicated the feasibility of magnetic separation of the synthesized catalysts. A long duration test indicated that the catalyst exhibits stability throughout the degradation reaction, as more than 80% of IBP was degraded after 300 minutes. The photocatalytic activity was directly affected by the ferrite load. The higher the nominal load of ferrite, the lower the performance in IBP degradation. It was also observed that the smallest amount of ferrite studied was enough for the catalyst to be recovered and reused. The adsorption and photolysis tests did not show significant results in the IBP degradation. In addition, it was possible to verify that the aqueous matrix, the use of solar radiation and the addition of additive (acid formic) were interfered directly in the process. The catalyst reuse tests indicated that it can be recovered and reused at least three times without considerable catalytic activity loss.

Chemico-nanotreatment methods for the removal of persistent organic pollutants and xenobiotics in water - A review

While the technologies available today can generate high-quality water from wastewater, the majority of the wastewater treatment plants are not intended to eliminate emerging xenobiotic pollutants, pharmaceutical and personal care items. Most endocrine disrupting compounds (EDCs) and personal care products (PPCPs) are more arctic than most regulated pollutants, and several of them have acid or critical functional groups. Together with the trace occurrence, EDCs and PPCPs create specific challenges for removal and subsequent improvements of wastewater treatment plants. Various technologies have been investigated extensively because they are highly persistent which leads to bioaccumulation. Researchers are increasingly addressing the human health hazards of xenobiotics and their removal. The emphasis of this review was on the promising methods available, especially nanotechnology, for the treatment of xenobiotic compounds that are accidentally released into the setting. In terms of xenobiotic elimination, nanotechnology provides better treatment than chemical treatments and their degradation mechanisms are addressed.

A novel ternary heterogeneous TiO2/BiVO4/NaY-Zeolite nanocomposite for photocatalytic degradation of microcystin-leucine arginine (MC-LR) under visible light

Microcystin-leucine arginine (MC-LR) is a carcinogenic toxin, produced by cyanobacteria. The release of this toxin into drinking water sources can threaten public health and environmental safety. Therefore, effective MC-LR removal from water resources is necessary. In the present study, the hydrothermal method was used to synthesize a novel ternary BiVO₄/TiO₂/NaY-Zeolite (B/T/N-Z) nanocomposite for MC-LR degradation under visible light. FESEM, FTIR, XRD, and DRS were performed for characterizing the nanocomposite structure. Also, the Response Surface Methodology (RSM) was applied to determine the impact of catalyst dosage, pH, and contact time on the MC-LR removal. High-performance liquid chromatography was performed to measure the MC-LR concentration. Based on the results, independent parameters, including contact time, catalyst dosage, and pH, significantly affected the MC-LR removal (P < 0.05). In other words, increasing the contact time, catalyst dosage, and acidic pH had positive effects on MC-LR removal. Among these variables, the catalyst dosage, with the mean square and F-value of 1041.37 and 162.84, respectively, had the greatest effect on the MC-LR removal efficiency. Apart from the interaction between the catalyst dosage and contact time, the interaction effects of other parameters were not significant. Also, the maximum MC-LR removal efficiency was 99.88% under optimal conditions (contact time = 120 min, catalyst dosage = 1 g/L, and pH = 5). According to the results, the B/T/N-Z nanocomposite, as a novel and effective photocatalyst could be used to degrade MC-LR from polluted water.

Ag0/Au0 nanocluster loaded Bi2O4 photocatalyst for methyl orange dye photodegradation

Visible-light-sensitive Ag and Au nanocluster loaded Bi₂O₄ (Ag–Bi₂O₄ and Au–Bi₂O₄) semiconductor photocatalysts have been synthesized. The composite materials exhibited increased photocatalytic degradation of the azo-dye pollutant, Methyl Orange (MO). In addition, Au–Bi₂O₄ (Au-7% wt) showed the highest MO degradation rate (0.05904 min⁻¹) i.e. 7.69 times higher than the pristine Bi₂O₄ and 1.4 times higher than 1% Ag–Bi₂O₄. The optical properties of the composites showed that the band gaps of the composite samples 1% Ag–Bi₂O₄ and 7% Au–Bi₂O₄ were 1.96 eV and 2.09 eV, respectively. The increase in the degradation rate is attributed to the decrease of the recombination rate of photoinduced e⁻/h⁺, caused by the enhanced charge transfer between the metal nanoparticles and Bi₂O₄ as confirmed in the photocurrent measurements. The photocurrent measurements showed increase in the transients output by 8.25 times and 2.75 times for 1% Ag–Bi₂O₄ & 3% Au–Bi₂O₄, respectively as compared to that of the pristine Bi₂O₄. These features further aided the increase in the photocatalytic efficiency while retaining the original physical properties, thus showing the robustness of Bi₂O₄ as a photocatalyst.

Illustration of charge transfer between Bi₂O₄ and nanoclusters, and photocatalytic MO degradation by M/Bi₂O₄ under visible light irradiation (M = Ag or Au).

Dynamic Stability Analysis in Hybrid Nanocomposite Polymer Beams Reinforced by Carbon Fibers and Carbon Nanotubes

The objective of this innovative research is assessment of dynamic stability for a hybrid nanocomposite polymer beam. The considered beam formed by multiphase nanocomposite, including polymer–carbon nanotubes (CNTs)–carbon fibers (CFs). Hence, as to compute the effective material characteristics related to multiphase nanocomposite layers, the Halpin–Tsai model, as well as micromechanics equations are employed. To model the structure realistically, exponential shear deformation beam theory (ESDBT) is applied and using energy methods, governing equations are achieved. Moreover, differential quadrature method (DQM) as well as Bolotin procedures are used for solving the obtained governing equations and the dynamic instability region (DIR) relative to the beam is determined. To extend this novel research, various parameters pinpointing the influences of CNT volume fraction, CFs volume percent, boundary edges as well as the structure’s geometric variables on the dynamic behavior of the beam are presented. The results were validated with the theoretical and experimental results of other published papers. The outcomes reveal that increment of volume fraction of CNT is able to shift DIR to more amounts of frequency. Further, rise of carbon fibers volume percent leads to increase the excitation frequency of this structure.

Removal of Diclofenac in Effluent of Sewage Treatment Plant by Photocatalytic Oxidation

Diclofenac (DCF) has been widely found in sewage treatment plants and environmental water bodies, and has attracted worldwide attention. In this paper, the photocatalytic degradation of DCF was investigated using a laboratory-scale simulated solar experimental device. This study focused on exploring the effects of the actual secondary effluent from sewage treatment plants (SE-A and SE-B) on the photocatalytic degradation of DCF and the changes of dissolved organic matter (DOM) during the photocatalytic degradation process. The results showed when SE-A and SE-B were used as the background water of the DCF solution, they displayed a significant inhibitory effect on the degradation of DCF, and the values of k were 0.039 and 0.0113 min−1, respectively. Among them, DOM played a major inhibitory role in photocatalytic degradation of DCF in sewage. In the photocatalytic process, the biological toxicity of the DCF solution was the least after 30 min of reaction, and then gradually increased. Furthermore, the organic matters in the sewage were greatly degraded after the photocatalytic reaction, including 254 and 365 nm ultraviolet (UV254, UV365) and chemical oxygen demand (COD). Moreover, titanium dioxide (TiO2) first catalyzed the degradation of macromolecular organic matters, and then degraded the small molecular organic matters.

Recent advances in the removal of persistent organic pollutants (POPs) using multifunctional materials:a review

Persistent organic pollutants (POPs) have gained heightened attentions in recent years owing to their persistent property and hazard influence on wild life and human beings. Removal of POPs using varieties of multifunctional materials have shown a promising prospect compared with conventional treatments. Herein, three main categories, including thermal degradation, electrochemical remediation, as well as photocatalytic degradation with the use of diverse catalytic materials, especially the recently developed prominent ones were comprehensively reviewed. Kinetic analysis and underlying mechanism for various POPs degradation processes were addressed in detail. The review also systematically documented how catalytic performance was dramatically affected by the nature of the material itself, the structure of target pollutants, reaction conditions and treatment techniques. Moreover, the future challenges and prospects of POPs degradation by means of multiple multifunctional materials were outlined accordingly. Knowing this is of immense significance to enhance our understanding of POPs remediation procedures and promote the development of novel multifunctional materials.

Photodecomposition of ibuprofen over g-C3N4/Bi2WO6/rGO heterostructured composites under visible/solar light

A microwave-assisted hydrothermal preparation of heterostructured graphitic carbon nitride/bismuth tungsten oxide/reduced graphene oxide nanocomposites (denoted as GBR-T, T = microwave irradiation time) is performed. The prepared GBR-T photocatalysts are identified by employing X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), time-resolved photoluminescence (TRPL) and nitrogen adsorption-desorption isotherms. The photocatalytic performance of these GBR-T is evaluated by the photocatalytic degradation of ibuprofen (IBP) under the visible light (λ > 420 nm) and solar light irradiation. Among all prepared photocatalysts, ca. 93% of IBP photodegradation can be achieved with a degradation rate constant (k) of 0.011 min^-1 under visible-light irradiation upon the optimal microwave-assisted reaction time of 60 min. The improvement is primarily attributable to the higher crystallization degree, specific surface area and increased charge transfer efficiency as verified by XRD, nitrogen adsorption-desorption isotherms and TRPL, respectively. The photocatalytic performance of this catalyst is further enhanced in the photodecomposition of IBP (ca. 98.6%) under sun light irradiation. The electron spin resonance (ESR) and liquid chromatography-mass/mass spectrometry (LC-MS/MS) studies show that the superoxide radicals and hydroxyl radicals are the dominant active species in the photocomposition of IBP and degradation intermediates are formed through three probable photodegradation pathways. This investigation provides a simple way to prepare triple 2D heterojuction photocatalysts which could be effectively used in the advanced oxidation process for removal of emerging contaminants in wastewater by using renewable energy.

Recent developments and challenges in practical application of visible-light-driven TiO2-based heterojunctions for PPCP degradation: A critical review

The ability of the TiO₂-based photocatalysis process to mineralize organic pollutants has attracted attention worldwide for the degradation of recalcitrant pharmaceuticals and personal care products (PPCPs). Nevertheless, (1) the limited exploitation of the solar spectrum, i.e., activation under UV light (only 2-3% of solar spectrum), and (2) the high recombination rate of photo-generated charge carriers, i.e., electrons and holes, have limited its application which can, however, be improved by developing a TiO₂-based heterojunction. The objective of this critical review paper is to discuss the recent developments (2009-2019) in visible-light-driven (VLD) TiO₂-based heterojunctions for PPCP degradation and their degradation mechanisms. Compared to the conventional heterojunctions, Schottky and Z-scheme heterojunctions, which are non-conventional heterojunctions, are found to be more effective for PPCP degradation due to their more efficient separation of charge carriers and the occurrence of redox reactions at a relatively higher redox potential. Furthermore, the enhancement strategies for the development of a VLD TiO₂-based heterojunction are also explored which can be achieved by selecting the (1) highly photocatalytically active {001} facet of anatase TiO₂, (2) synthesis methods governing the structural changes at the junction interface, and (3) heterojunction components which can efficiently generate the powerful •OH radicals. The challenges in practical applications are also discussed which include factors, viz., cost reduction, recycling, stability, byproducts analysis, evaluation of the environmental effectiveness, and reactor design and scale-up of the VLD TiO₂-based heterojunctions. Accordingly, the prospects of VLD TiO₂-based heterojunctions for PPCP degradation in real environmental applications are discussed.

Phosphate-modified m-Bi2O4 enhances the absorption and photocatalytic activities of sulfonamide: Mechanism, reactive species, and reactive sites

Widespread usage of the sulfonamide class of antibiotics is causing increasing ecotoxicological concern, as they have the capacity to alter ambient ecosystems. Photocatalytic technology is an attractive yet challenging strategy for the degradation of antibiotics. For this work, the phosphate modification of m-Bi₂O₄ (Bi₂O₄-P) was prepared via a one-step hydrothermal process involving sodium bismuthate and sodium phosphate, which was employed for the degradation of sulfamethazine (SMZ) under visible light irradiation. The 0.5% Bi₂O₄-P exhibited excellent photocatalytic performance, which was 1.9 times that of pure m-Bi₂O₄. The photocatalytic degradation kinetics and mechanism of SMZ was investigated at different pH, whereupon it was revealed that m-Bi₂O₄-P exhibited improved SMZ adsorption and photocatalytic activities in contrast to pure m-Bi₂O₄. Compared with other four sulfonamide antibiotics, structures that contained additional methyl on the pyrimidine could be more easily attacked by phosphate modified m-Bi₂O₄. Reactive species (RS) scavenging experiments revealed that h⁺ was primarily responsible for the degradation of SMZ. Further studies of RS by ESR technology, and the results of photoelectrochemical properties showed phosphate-modified m-Bi₂O₄ could make greater use of photogenerated carriers, thereby producing additional RS. Based on the HRAM LC-MS/MS and the Frontier Molecular Orbital Theory, the degradation pathways of SMZ were proposed.

First-principles investigation of the electronic properties of the Bi2O4(101)/BiVO4(010) heterojunction towards more efficient solar water splitting

First-principles calculations based on density functional theory were carried out to explore the geometric structure, light absorption, charge separation, over-potential and stability of Bi₂O₄ (101)/BiVO₄ (010) heterojunction. The results show that the formed heterojunction can improve visible light utilization and promote transfer of photo-generated holes from BiVO₄ to Bi₂O₄. Furthermore, the Bi⁵⁺ site in the Bi₂O₄(101) surface is energetically more favorable as the photoanode for the oxygen evolution reaction (OER) than the Bi³⁺ sites in Bi₂O₄(101) and BiVO₄(010). At the same time, it is also found that the Bi⁵⁺ in Bi₂O₄(101) are more stable than the Bi³⁺ due to the lower surface energy and stronger bond energy with neighbors. Therefore, forming the Bi₂O₄/BiVO₄ heterojunction can effectively improve the activity and stability of BiVO₄ for water splitting reactions.

Removal of Pharmaceutical Contaminants in Wastewater Using Nanomaterials: A Comprehensive Review

BACKGROUND

The limitless presence of pharmaceutical contaminants in discharged wastewater has emerged as a threat to aquatic species and humans. Their presence in drinking water has although raised substantial concerns, very little is known about the fate and ecological impacts of these pollutants. As a result, these pollutants are inevitably introduced to our food chain at trace concentrations. Unfortunately, the conventional wastewater treatment techniques are unable to treat pharmaceuticals completely with practical limitations. The focus has now been shifted towards nanotechnology for the successful remediation of these persistent pollutants. Thus, the current review specifically focuses on providing readers brief yet sharp insights into applications of various nanomaterials for the removal of pharmaceutical contaminants.

METHODS

An exhaustive collection of bibliographic database was done with articles having high impact and citations in relevant research domains. An in-depth analysis of screened papers was done through standard tools. Studies were categorized according to the use of nanoscale materials as nano-adsorbents (graphene, carbon nanotubes), nanophotocatalysts (metal, metal oxide), nano-filtration, and ozonation for promising alternative technologies for the efficient removal of recalcitrant contaminants.

RESULTS

A total of 365 research articles were selected. The contemporary advancements in the field of nanomaterials for drinking and wastewater treatment have been thoroughly analyzed along with their future perspectives.

CONCLUSION

The recommendations provided in this article will be useful to adopt novel strategies for on-site removal of the emerging contaminants in pharmaceutical effluents and related industries.

Construction of a rod-like Bi2O4 modified porous g-C3N4 nanosheets heterojunction photocatalyst for the degradation of tetracycline

The solar-powered semiconductor photocatalytic technology for pollutant degradation has been widely studied for its potential to alleviate the current environmental crisis.

Unravelling mechanistic reasons for differences in performance of different Ti- and Bi-based magnetic photocatalysts in photocatalytic degradation of PPCPs

Despite numerous developments in the field of heterogeneous photocatalysis, particularly its environmental applications, there remain fundamental uncertainties regarding the key properties which primarily govern the performance of a photocatalyst. In this study, four visible-light-driven magnetic photocatalysts, viz., Ag/Fe,N-TiO₂/Fe₃O₄@SiO₂, g-C₃N₄/TiO₂/Fe₃O₄@SiO₂, BiOBr/Fe₃O₄@SiO₂, and BiOBr_0.9I_0.1/Fe₃O₄@SiO₂, were synthesized and comparatively studied in terms of their material characteristics, charge transfer efficiency, and photocatalytic performance in the degradation of two model pharmaceuticals and personal care products (PPCPs), ibuprofen and benzophenone-3. Amongst the tested photocatalysts, the g-C₃N₄/TiO₂/Fe₃O₄@SiO₂ exhibited the fastest degradation kinetics for both the PPCPs. Property-performance relationships were evaluated in which the dependence of the photocatalytic performance on various adsorption-related, electronic band-structure-related, reactive species-related, and charge carriers-related properties was examined. The strongest performance relationship was found to be with photocurrent density-an indicator of charge transfer efficiency-for both PPCPs, indicating its influential role in governing the photocatalytic performance. The findings unfold a potential research direction towards exploration of factors which can enhance the charge transfer efficiency, thereby possibly enabling the rational design of highly efficient photocatalysts for PPCPs removal.

Pharmaceutically active compounds in aqueous environment: A status, toxicity and insights of remediation

Pharmaceutically active compounds (PhACs) have pernicious effects on all kinds of life forms because of their toxicological effects and are found profoundly in various wastewater treatment plant influents, hospital effluents, and surface waters. The concentrations of different pharmaceuticals were found in alarmingly high concentrations in various parts of the globe, and it was also observed that the concentration of PhACs present in the water could be eventually related to the socio-economic conditions and climate of the region. Drinking water equivalent limit for each PhAC has been calculated and compared with the occurrence data from various continents. Since these compounds are recalcitrant towards conventional treatment methods, while advanced oxidation processes (AOPs) have shown better efficiency in degrading these PhACs. The performance of the AOPs have been evaluated based on percentage removal, time, and electrical energy consumed to degrade different classes of PhACs. Ozone based AOPs were found to be favorable because of their low treatment time, low cost, and high efficiency. However, complete degradation cannot be achieved by these processes, and various transformation products are formed, which may be more toxic than the parent compounds. The various transformation products formed from various PhACs during treatment have been highlighted. Significant stress has been given on the role of various process parameters, water matrix, oxidizing radicals, and the mechanism of degradation. Presence of organic compounds, nitrate, and phosphate usually hinders the degradation process, while chlorine and sulfate showed a positive effect. The role of individual oxidizing radicals, interfering ions, and pH demonstrated dissimilar effects on different groups of PhACs.

Visible-light-driven N-TiO2@SiO2@Fe3O4 magnetic nanophotocatalysts: Synthesis, characterization, and photocatalytic degradation of PPCPs

TiO₂-based photocatalysis offers certain advantages like rapid degradation and mineralization of organic compounds. However, the practical applicability of photocatalysts in degradation of pharmaceuticals and personal care products (PPCPs) is still restricted by challenges including their limited photocatalytic activity under visible light and difficulty in their separation from suspension. To overcome these challenges, a visible-light-driven magnetic N-TiO₂@SiO₂@Fe₃O₄ nanophotocatalyst was developed through fine-tuning the pertinent factors (calcination temperature, Fe₃O₄ loading, and nitrogen doping) involved during synthesis process, on the basis of degradation of ibuprofen (a typical PPCP). The TEM-EDX, XRD and XPS analyses confirmed the successful synthesis of nanophotocatalyst. By comparing nanophotocatalyst's performance on ibuprofen under two visible light sources, i.e., compact fluorescent lamps (CFLs) and light emitting diodes (LEDs) of similar irradiance, CFLs of irradiance 320μWcm^-2 and peak emissive wavelength 543nm served as a better source, resulting in 94% degradation. Furthermore, 93% of benzophenone-3 within 5h and 71% of carbamazepine within 9h was degraded under visible light emitted by CFLs. The superparamagnetic behavior of the nanophotocatalyst enabled its successful magnetic separation (95% efficiency) from the suspension within 20-25min under an electromagnetic field of ∼200mT.

Enhanced visible light photoreduction of aqueous Cr(VI) by Ag/Bi4O7/g-C3N4 nanosheets ternary metal/non-metal Z-scheme heterojunction

In this paper, we successfully constructed a ternary metal/non-metal nanomaterial which can synergize Z-scheme heterojunction and plasmonic metal/semiconductor for enhancing visible light photoreduction of aqueous Cr(VI). The as-formed ternary metal/non-metal nanomaterial was composed of g-C₃N₄ nanosheets mutual modified by Ag nanoparticles and Bi₄O₇. In the ternary nanomaterial, g-C₃N₄ nanosheets and Bi₄O₇ fabricated Z-scheme heterojunction, g-C₃N₄ nanosheets and Ag nanoparticles formed plasmonic metal/semiconductor system, synchronously. The photodeposition experiments were designed to indirect demonstrate the Z-scheme heterojunction via photocatalytic oxidation and reduction deposition reactions, AgNO₃ was used as the electron acceptor and Pb(NO₃)₂ as the electron donor, photocatalytic reduction product and oxidation product were selectively deposited on g-C₃N₄ nanosheets and Bi₄O₇, respectively, revealing the Z-scheme heterojunction was definite formed. In addition, X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), UV-vis absorption, and Fourier-transform infrared spectroscopy (FTIR) were studied to indicate that the plasmonic metal/semiconductor system was existent in the ternary nanomaterial. The visible light photoreduction of ternary Ag/Bi₄O₇/g-C₃N₄ nanosheets was evaluated by photoreducing aqueous Cr(VI). The photoreduction results show that the ternary Ag/Bi₄O₇/g-C₃N₄ nanosheets is much higher than the pristine bulk g-C₃N₄ and g-C₃N₄ nanosheets.

Reusable magnetic Ag/Fe, N-TiO2/Fe3O4@SiO2 composite for simultaneous photocatalytic disinfection of E. coli and degradation of bisphenol A in sewage under visible light

A visible-light-driven and magnetic photocatalyst Ag/Fe,N-TiO₂/Fe₃O₄@SiO₂ (AgFeNTFS) was synthesized through a multi-step method. AgFeNTFS was tested for the photocatalytic disinfection of Escherichia coli (E. coli) and degradation of bisphenol A (BPA) under visible light irradiation, separately and simultaneously. The results showed that a 6.3-log reduction in cell density of E. coli was achieved and BPA (2 mg/L) was completely removed by AgFeNTFS in the separated photocatalytic processes within 120 min. In the simultaneous process, the photocatalytic disinfection of E. coli was not influenced in the presence of BPA, but the efficiency of BPA degradation was dropped by 10%. This was likely due to the competition for the same dominant reactive species of O₂^- and H₂O₂ between E. coli and BPA in the simultaneous process, as evidenced by the scavenger study and the interactions between the pollutants and AgFeNTFS. Moreover, the simultaneous photocatalytic activity of E. coli disinfection and BPA degradation by AgFeNTFS was investigated in the sewage obtained from a local wastewater treatment plant. The photocatalysis treated sewage could meet with the local disinfection discharge standard with a 3-log reduction of E. coli after 90 min, and a complete removal of BPA was achieved simultaneously after 360 min. Moreover, AgFeNTFS showed high magnetic separation efficiency and had a good reusability over three cycles for the simultaneous photocatalytic disinfection and degradation of BPA in both synthetic water and sewage. This study provides insights on the application of a reusable magnetic photocatalyst for simultaneous disinfection and degradation of BPA in sewage.

Heterogeneous photocatalysis and its potential applications in water and wastewater treatment: a review

There has been a considerable amount of research in the development of sustainable water treatment techniques capable of improving the quality of water. Unavailability of drinkable water is a crucial issue especially in regions where conventional drinking water treatment systems fail to eradicate aquatic pathogens, toxic metal ions and industrial waste. The research and development in this area have given rise to a new class of processes called advanced oxidation processes, particularly in the form of heterogeneous photocatalysis, which converts photon energy into chemical energy. Advances in nanotechnology have improved the ability to develop and specifically tailor the properties of photocatalytic materials used in this area. This paper discusses many of those photocatalytic nanomaterials, both metal-based and metal-free, which have been studied for water and waste water purification and treatment in recent years. It also discusses the design and performance of the recently studied photocatalytic reactors, along with the recent advancements in the visible-light photocatalysis. Additionally, the effects of the fundamental parameters such as temperature, pH, catalyst-loading and reaction time have also been reviewed. Moreover, different techniques that can increase the photocatalytic efficiency as well as recyclability have been systematically presented, followed by a discussion on the photocatalytic treatment of actual wastewater samples and the future challenges associated with it.

Orthogonal synthesis of a novel hybrid layered material containing three different zincous components and its photocatalytic property investigation

A novel hybrid layered material-Schiff Base-Zinc Complexes intercalated ZnCr-LDHs-supported ZnO-was synthesized by one-step coprecipitation method and characterized by XRD, UV-vis DRS, SEM, TEM, BET, ICP-AES and XPS analysis. The influences of the three Zn components (intercalated between the layers, supported on the surface, distributed in the host layers of the layered material) on the crystallinity and the photocatalytic activity of ZnO/ZnCr-SalenZn-LDHs for Rhodamine B (RhB) degradation were studied in detail by orthogonal design. The results showed that the percentage of the three components has a great effect on the structure and photocatalytic performance of ZnO/ZnCr-SalenZn-LDHs. The SalenZn intercalated between the layers and the Zn distributed in the layers of the layered material were the main influencing factors, and the ZnO supported on the surface of the layered material was the secondary influencing factor. The optimum initial molar ratios were SalenZn:Cr = 0.5, Zn:Cr = 3, and ZnO:Cr = 0.75, respectively, and the photocatalytic degradation efficiency of RhB reached 96.9%. In addition, a possible mechanism of photocatalysis was discussed from the perspectives of photogenerated reactive species and photoinduced carries transfer. While, the regeneration of the best photocatalytic material was also investigated in detail.