Simultaneous and efficient photocatalytic reduction of Cr(VI) and oxidation of trace sulfamethoxazole under LED light by rGO@Cu2O/BiVO4p-n heterojunction composite

The self-boosting ultrafast removal of Cr(VI) and organic dye in textile wastewater through sulfite-induced redox processes

The treatment of textile wastewater containing harmful metal ions poses a significant challenge in industrial applications due to its environmental impact. In this study, the use of sulfite for treating simulated dye wastewater containing New Coccine (NC) and Cr(VI) was investigated. The removal of NC was influenced by the redox reaction between Cr(VI) and sulfite, demonstrating a strong self-boosting effect of Cr(VI) on NC removal. Remarkable NC decoloration (95%) and Cr(VI) reduction (90%) were achieved within 1 min, highlighting the effectiveness of the treatment. Quenching experiments and electron paramagnetic resonance (EPR) technology confirmed that singlet oxygen (1O2) was the main oxidative agent for organic dye removal and SO4•-, •OH and Cr(V) were also identified as key contributors to NC degradation. The Cr(VI)/sulfite system exhibited higher efficiency in degrading azo dyes, such as NC and Congo Red (CR), compared to non-azo dyes like Methylene Blue (MB). This superiority may be attributed to the action of Cr(V) on azo groups. Additionally, the COD removal experiments were conducted on the actual dye wastewater, showing the excellent performance of the Cr(VI)/Sulfite system in treating industrial textile wastewater. This approach presents a promising strategy for effective "waste control by waste", offering great potential for addressing challenges related to dye wastewater treatment and environmental pollution control in practical industrial scenarios.

Synchronous removal of oxytetracycline and Cr(Ⅵ) in Fenton-like photocatalysis process driven by MnFe2O4/g-C3N4: Performance and mechanisms

Complex wastewater has more complicated toxicity and potential harm to organisms, and synchronous REDOX of complex pollutants in wastewater has always been a bottleneck in the development of advanced oxidation technology. Herein, a Fenton-like photocatalytic system (MnFe2O4/g-C3N4 heterojunction composites) was established to simultaneously remove oxytetracycline (OTC) and Cr(Ⅵ) in this study. The MnFe2O4/g-C3N4 heterojunction composites exhibited outstanding catalytic performances for OTC and Cr(Ⅵ) removal, and more than 90% of OTC and nearly 100% of Cr(Ⅵ) were simultaneously removed within 1 min photocatalysis. The photo-generared electrons and holes played significant roles in Cr(Ⅵ) reduction and OTC degradation, respectively. Moreover, the heterojunction formed between g-C3N4 and MnFe2O4 effectively accelerated the separation and migration of photogenerated carriers. The OTC degradation was mainly initiated by cracking of benzene rings, degradation of substituents, and removal of groups such as -OH, -NH2, -CH3, and -CONH2, resulting in generation of small molecular substances; Cr(Ⅲ) was the main reduction product of Cr(Ⅵ). Meanwhile, the MnFe2O4/g-C3N4 heterojunction composites also exhibited excellent stability and reusability in removal of OTC and Cr(Ⅵ).

Ag2O@UiO-66 new thin film as p-n heterojunction: permanent photoreduction of hexavalent Cr

The new nanosphere Ag2O@UiO-66 thin-film was synthesized on a stainless steel mesh surface via an electrophoretic deposition method, and is used as an effective and low-cost photocatalyst using visible light. The synthesized nanocomposite was used to perform photo-reduction of Cr(vi) ions under white light irradiation. The best removal rate (72% after 15 minutes) was obtained by the film with 0.034 grams of deposited composite having relative percentages of Ag2O : UiO-66 of 70 : 30. The interesting obtained results confirm that the p-n heterojunction of the composite is the main cause of the desired charge separation and the photoreduction speed increase. In the following, the resulting compounds were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmittance electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy diffraction X-ray spectroscopy (EDAX) and the Brunauer, Emmett, and Teller (BET) method. Scavenging studies performed in the presence of familiar scavengers confirmed that superoxide radicals (˙O2-) and dissolved oxygen gas have a significant role in the photocatalytic reduction process.

Effective photodegradation of antibiotics by guest-host synergy between photosensitizer and bismuth vanadate: Underlying mechanism and toxicity assessment

The removal of antibiotics in wastewater has attracted increasing attention. Herein, a superior photosensitized photocatalytic system was developed with acetophenone (ACP) as the guest photosensitizer, bismuth vanadate (BiVO₄) as the host catalyst and poly dimethyl diallyl ammonium chloride (PDDA) as the bridging complex, and used for the removal of sulfamerazine (SMR), sulfadiazine (SDZ) and sulfamethazine (SMZ) in water under simulated visible light (λ > 420 nm). The obtained ACP-PDDA-BiVO₄ nanoplates attained a removal efficiency of 88.9%-98.2% for SMR, SDZ and SMZ after 60 min reaction and achieved kinetic rate constant approximately 10, 4.7 and 13 times of BiVO₄, PDDA-BiVO₄ and ACP-BiVO₄, respectively, for SMZ degradation. In the guest-host photocatalytic system, ACP photosensitizer was found to have a great superiority in enhancing the light absorption, promoting the surface charge separation-transfer and efficient generation of holes (h⁺) and superoxide radical (·O₂^-), greatly contributing to the photoactivity. The SMZ degradation pathways were proposed based on the identified degradation intermediates, involving three main pathways of rearrangement, desulfonation and oxidation. The toxicity of intermediates was evaluated and the results demonstrated that the overall toxicity was reduced compared with parent SMZ. This catalyst maintained 92% photocatalytic oxidation performance after five cyclic experiments and displayed a co-photodegradation ability to others antibiotics (e.g., roxithromycin, ciprofloxacin et al.) in effluent water. Therefore, this work provides a facile photosensitized strategy for developing guest-host photocatalysts, which enabling the simultaneous antibiotics removal and effectively reduce the ecological risks in wastewater.

An in-depth insight into the simultaneous oxidation of sulfamethoxazole and reduction of Cr (VI) by one system of water film DBD plasma: The interaction effect, role of active species, and their dominant to pathways

This study aims to deeply investigate the simultaneous elimination of sulfamethoxazole (SMZ) and Cr (VI) through one system of water film dielectric barrier discharge (WFDBD) plasma. The interaction effect of SMZ degradation and Cr (VI) reduction and dominant effect of active species were highlighted. Results showed that the oxidation of SMZ and the reduction of Cr (VI) directly promote each other. When the concentration of Cr (VI) raised from 0 to 2 mg L^-1, the degradation rate of SMZ enhanced from 75.6% to 88.6%, respectively. Similarly, when the concentration of SMZ improved from 0 to 15 mg L^-1, the removal efficiency of Cr (VI) improved from 70.8% to 84.3%, respectively. ·OH, ¹O₂ and ·O₂^- play crical roles for SMZ degradation, and e^-, ·O₂^-, ·H and H₂O₂ dominated to the Cr (VI) reduction. The variations of pH, conductivity and TOC during the removal process were also explored. The removal process was studied by UV-vis spectroscopy and a three-dimensional excitation-emission matrix. Based on DFT calculation and LC-MS analysis, free radicals dominated SMZ degradation pathways in the WFDBD plasma system were clarified. Besides, the influence of Cr (VI) on SMZ degradation pathway was clarified. The ecotoxicity of SMZ and the toxicity of Cr (VI) into Cr (III) were greatly reduced. This study provides a significant reference value for the application and mechanism of plasma simultaneous removal of organic pollutants and heavy metals in wastewater.

Pd nanoparticles decorated BiVO4 pine architectures for photocatalytic degradation of sulfamethoxazole

Sulfamethoxazole (SMX) has been extensively detected in wastewater treatment plant effluents and surface water. Because of its potential risks to ecology and health, treatment for eliminating SMX is urgently required. In this study, we report the application of Pd nanoparticles decorated on BiVO₄ pine architecture for the photocatalytic degradation of SMX. The results showed that the barer BiVO₄ and Pd-BiVO₄ eliminated SMX under visible-light irradiation. After 210 min of irradiation, 98.8% of SMX was substantially eliminated by Pd-BiVO₄, whereas bare BiVO₄ can degraded approximately 36.3% of SMX. Pd-BiVO₄ also exhibited a high mineralization rate (84% of total organic carbon (TOC) removal) compared to bare BiVO₄ (51% of TOC removal). Through three-dimensional excitation-emission matrix fluorescence spectra, SMX with high fluorescence intensity can be degraded to non-fluorescence intermediate products, further confirming the high mineralization of SMX over Pd-BiVO₄ catalyst. Well-dispersed Pd nanoparticles on the {040} facet of BiVO₄ pine architecture can support the recombination of photogenerated charge carriers because of the formation of the Schottky junction at the Pd-BiVO₄ interface. Besides, the active species trapping tests indicated that ^•O₂^- and h⁺ radicals dominate SMX photodegradation over Pd-BiVO₄. The main degradation intermediates of SMX in the reaction solution was also identified through ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry analysis. This investigation can provide insight into designing metallic/semiconductor junctions for antibiotic elimination in water media.

CuO improved energy band of AgO/fibrous SiO2-ZrO2 for optimized simultaneous photocatalytic redox of chromium (VI) and p-cresol using response surface methodology

Ternary CuO/AgO/FSZr photocatalysts were fabricated via the hydrothermal and electrochemical methods with three different CuO loading (1, 3 and 5 wt%), indicated as 1CuO/AgO/FSZr, 3CuO/AgO/FSZr and 5CuO/AgO/FSZr. The photocatalytic reaction was tested towards simultaneous chromium (VI) photoreduction and p-cresol photooxidation and the performance in order as follow: 3CuO/AgO/FSZr > 5CuO/AgO/FSZr > 1CuO/AgO/FSZr > AgO/FSZr > FSZr. CuO/AgO/FSZr photocatalysts showed an improvement in photocatalytic activity compared to AgO/FSZr and FSZr due to the reduction potential of chromium (VI) aligned closer to the conduction band of CuO and provided abundant free active electrons (e^-) and holes (h⁺) with efficient transportation and migration. Interestingly, the 3CuO/AgO/FSZr was established as the best photocatalyst with 98% reduction of chromium (VI) and 83% oxidation of p-cresol simultaneously, owing to its strong corporation between the metal oxides and support and higher total pore volume. The Langmuir-Hinshelwood model were employed for kinetics which followed the pseudo-first-order kinetics model well. Based on the simultaneous photocatalytic mechanism, chromium (VI) and p-cresol were directly reduced and oxidized by e^- and h⁺, respectively. The response surface methodology (RSM) discovered that the quadratic term initial concentration of chromium (VI) is the main significant factor in photocatalytic performance. The optimum parameters for simultaneous photoredox of chromium (VI) and p-cresol predicted from RSM are 9.6 mg L^-1 of chromium (VI) concentration, 9.8 mg L^-1 of p-cresol concentration and 0.32 g L^-1 of catalyst dosage. Under these conditions the error between the predicted and experimental values is only 3.7%. The 3CuO/AgO/FSZr sustained the photocatalytic performance after reused for five cycles and could oxidized various organic pollutants as well as reduced chromium (VI) simultaneously.

Properties and mechanism of Cr(VI) removal by a ZnCl2-modified sugarcane bagasse biochar-supported nanoscale iron sulfide composite

A ZnCl₂-modified biochar-supported nanoscale iron sulfide composite (FeS-ZnBC) was successfully prepared to address the easy oxidization of FeS and enhance Cr(VI) removal from water. The material was characterized by SEM, XRD, FTIR, and XPS. The effects of FeS:ZnBC mass ratio, FeS-ZnBC dosage, solution pH, initial Cr(VI) concentration, and reaction time on the adsorption performance were investigated. The results revealed that the optimum adsorption capacity of FeS-ZnBC (FeS:ZnBC = 1:2) for Cr(VI) was 264.03 mg/g at 298 K (pH = 2). A Box-Behnken design (BBD) was applied to optimize the input variables that affected the adsorption of Cr(VI) solution. The results revealed that the highest removal (99.52%) of Cr(VI) solution was achieved with a Cr(VI) initial concentration of 150.59 mg/L, FeS-ZnBC adsorbent dosage of 2 g/L, and solution pH of 2. The sorption kinetics could be interpreted using a pseudo-second-order kinetic model. The isotherms were simulated using the Redlich-Peterson isotherm model, indicating that Cr(VI) removal by the FeS-ZnBC composites was a hybrid chemical reaction-sorption process. The main mechanisms of Cr(VI) removal by FeS-ZnBC were adsorption, chemical reduction, and complexation. This study demonstrated that FeS-ZnBC has potential application prospects in Cr(VI) removal.

Removal of Cr(VI) from aqueous solution by a novel ZnO-sludge biochar composite

The incorporation of ZnO into biochar has become a promising way to obtain adsorbents with enhanced adsorption capacity. In this study, a low-cost ZnO-sludge biochar composite (ZBC) was prepared by a simply in situ method using sewage sludge biochar (SBC) and zinc acetate, as well as employed for Cr(VI) adsorption in water. The results of XPS and FT-IR suggested that the ZBC surface had more functional groups such as -COOH, -OH, -C-O, ZnO, etc. Compared with SBC, the BET-specific surface area of the ZBC increased from 8.82 to 41.24 m²·g^-1, which provides potential advantages for Cr(VI) uptake. Benefiting from ZnO incorporation, about an 18% increase in Cr(VI) removal efficiency was obtained. The maximum removal efficiency and equilibrium adsorption amount of ZBC for Cr(VI) reached 98.4% and 33.87 mg·g^-1, respectively. The adsorption was spontaneous and endothermic nature, and coincided nicely with pseudo-second-order kinetics and Langmuir isotherm. The analyses indicated that Cr(VI) removal by ZBC was predominantly via electrostatic attraction, surface complexation, ion exchange, and reduction. This study provided valuable insights into the problem of sludge disposal and provided a new and effective method for Cr(VI) removal.

Boosting the photocatalytic performance of Bi2Fe4O9 through formation of Z-scheme heterostructure with In2S3: Applications towards water decontamination

Design of biocompatible nano-heterostructure photocatalyst with broad UV-visible spectrum response and strong redox ability is a promising approach with potential application in micropollutant degradation and pathogen deactivation from aqueous sources. Herein, we have reported the facile fabrication of In₂S₃/Bi₂Fe₄O₉ (ISxBFO) binary heterostructure by hydrothermally depositing In₂S₃ nanoparticles (20-40 nm) over Bi₂Fe₄O₉ nanocuboids/nanoplates prepared by combustion synthesis route. In depth characterization study revealed broad spectrum UV-Vis absorption, large interfacial contact, improved charge carrier separation and mobility and a longer excited state life time (4.7 ns) for the ISxBFO heterostructure materials. The integration of In₂S₃ with Bi₂Fe₄O₉ strongly boosts the optoelectrical and photocatalytic property of pristine Bi₂Fe₄O₉. The ISxBFO heterostructure material exhibited enhanced photocatalytic efficiency for aqueous phase degradation of sulfamethoxazole antibiotics (k_app = 0.06 min^-1) and phenyl urea herbicides (k_app = 0.028 min^-1) with reaction rates 3-8 times higher than the pure BFO component. The MTT assay experiments confirmed non-cytotoxic nature of treated sulfamethoxazole and diuron solutions. The composite materials also displayed convincing antibacterial behavior towards toxigenic Vibrio cholerae pathogen. Haemagglutination assay study revealed excellent biocompatibility of the binary composite up to 200 mg L^-1. Radical trapping study suggested expeditious generation of ^•OH and ^•O₂^- radicals over the ISxBFO surface which is nearly 3.8 and 2.3 times higher than pure BFO and In₂S₃ respectively. The occurrence of a direct Z-scheme mechanism is inferred from radical trapping and XPS study which accounted for the improved photocatalytic activity and strong radical generation property of the ISxBFO heterostructure material.

Photocatalytic oxidation of glyphosate and reduction of Cr(VI) in water over ACF-supported CoNiWO4-gCN composite under batch and flow conditions

Photocatalytic treatment of wastewater using nanomaterials is an efficient energy saving technology. Yet the practical application of the technology is limited because of difficulty in developing the stable, supported photocatalytic nanoparticles that can be used under continuous flow conditions. Here, we report an efficient removal of glyphosate (GLP) and Cr(VI) from water under batch as well as continuous flow conditions using the activated carbon fiber (ACF)-supported nanocomposite of CoNiWO4 (CNW) and g-C3N4 (gCN), as a photocatalyst. CNW-gCN/ACF is synthesized using a one-step strategy, and spectroscopic characterization techniques are used to corroborate the formation of the Z-scheme-based CNW-gCN heterojunction in the ACF substrate. Efficacy of the photocatalyst is assessed in visible light irradiation. The batch activity data of the individual pollutant show the complete oxidation of GLP at 30 ppm and reduction of Cr(VI) at 200 ppm concentration levels in 60 and 150 min, respectively at 1 g/L dose of CNW-gCN/ACF. Photocatalytic efficiency of CNW-gCN/ACF in the simultaneous removal of both pollutants from co-contaminated feed is found to be greater than that in single-feed system under identical experimental conditions. Tested under flow conditions, CNW-gCN/ACF shows approximately the same rates of oxidation and reduction as prevalent under batch conditions, indicating the efficient immobilization of the nanocatalyst particles in ACF, which not only prevents elution of the catalyst but also improves its reusability. The toxicity data indicate the treated water samples to be non-toxic. The current study provides an efficient method for developing supported nanomaterial photocatalysts for treating flowing co-contaminated wastewater.

A review on synergistic coexisting pollutants for efficient photocatalytic reaction in wastewater remediation

With the tremendous development of the economy and industry, the pollution of water is becoming more serious due to the excessive chemical wastes that need to remove thru reduction or oxidation reactions. Simultaneous removal of dual pollutants via photocatalytic redox reaction has been tremendously explored in the last five years due to effective decontamination of pollutants compared to a single pollutants system. In a photocatalysis mechanism, the holes in the valence band can remarkably promote the oxidation of a pollutant. At the same time, photoexcited electrons are also consumed for the reduction reaction. The synergistic between the reduction and oxidation inhibits the recombination of electron-hole pairs extending their lifetime. In this review, the binary pollutants that selectively removed via photocatalysis reduction or oxidation are classified according to heavy metal-organic pollutant (HM/OP), heavy metal-heavy metal (HM/HM) and organic-organic pollutants (OP/OP). The intrinsic between the pollutants was explained in three different mechanisms including inhibition of electron-hole recombination, ligand to metal charge transfer and electrostatic attraction. Several strategies for the enhancement of this treatment method which are designation of catalysts, pH of mixed pollutants and addition of additive were discussed. This review offers a recent perspective on the development of photocatalysis system for industrial applications.

Removal of hexavalent chromium from water by Z-scheme photocatalysis using TiO2 (rutile) nanorods loaded with Au core-Cu2O shell particles

All-solid-state Z-scheme photocatalysts, containing Cu₂O, TiO₂ (rutile), and Au as the electron mediator, were prepared and applied to the reduction of Cr(VI) in aqueous solutions. The Cu₂O-Au-TiO₂ composites were prepared by loading Au core-Cu₂O shell hemisphere particles on TiO₂ (rutile) nanorods using a two-step photocatalytic deposition process. Under ultraviolet-visible (UV-vis) light illumination, the Cu₂O-Au-TiO₂ composites exhibited higher photocatalytic Cr(VI) reduction activities than those exhibited by single TiO₂ (rutile) and Cu₂O. In this reaction, a precipitate containing Cr, which was considered to be Cr(OH)₃, was deposited site-selectively on the Au core-Cu₂O shell particles of the composites, indicating that the reduction site of the composite was Cu₂O, and the reaction proceeded according to the Z-scheme. The Cu₂O-Au-TiO₂ composites also exhibited photocatalytic activity under visible light illumination. The oxidation state of Cu in the Cu₂O-Au-TiO₂ composite gradually changed from Cu(I) to Cu(II) during the photocatalytic Cr(VI) reduction. However the composite maintained its high photocatalytic performance even after oxidation. The role of Au in the Cu₂O-Au-TiO₂ composite was examined by comparing the properties of the Cu₂O-Au-TiO₂ composite with those of the Cu₂O-TiO₂ composite prepared via direct Cu₂O deposition on TiO₂.

Interfacial coupling effects on adsorptive and photocatalytic performances for photoresponsive graphene-wrapped SrTiO3@Ag under UV-visible light: experimental and DFT approach

Understanding the graphene/semiconductor/metal interactions is crucial to design innovative photocatalytic materials with efficient photocatalytic activity for environmental cleanup applications. SrTiO₃ on reduced graphene oxide (rGO) with various graphene contents was successfully synthesized in this study utilizing a simple hydrothermal method, followed by decorating the surface with Ag particles by using the photodeposition process. Under UV-visible light irradiation, the resulting composites were tested for their improved photocatalytic activity to decompose methylene blue (MB). The prepared photocatalysts were characterized by XRD, SEM, EDX, DLS, FT-IR, Raman spectroscopy, and DRS. First-principle density functional theory calculations (DFT) were also carried out by using the generalized gradient approximation (GGA) and PBE functional with the addition of on-site Coulomb correction (GGA + U). The obtained SrTiO₃/rGO@Ag composites showed great improvement in the photocatalytic performances over pristine SrTiO₃. For the degradation reaction of MB, SrTiO₃/rGO_20%@Ag_4% composites yielded the best photocatalytic activity with efficacy reach 94%, which was also shown that it could be recycled up to four times with nearly unchanged photocatalytic activity.

Extensive solar light utilizing by ternary C-dots/Cu2O/SrTiO3: Highly enhanced photocatalytic degradation of antibiotics and inactivation of E. coli

Fabrication of a visible-light driven photocatalyst is of great vital for the elimination of antibiotics and microorganism in the wastewater and the construction of sustainable green energy systems. In this work, carbon quantum dots (C-dots) were integrated with Cu₂O/SrTiO₃ p-n heterojunction to optimize the photocatalytic activity. The excellent photocatalytic degradation efficiency of chlortetracycline hydrochloride (CTC·HCl) (92.6% within 90 min) and E. coli inactivation efficiency were observed over C-dots/Cu₂O/SrTiO₃ under visible light irradiation. It is the synergistic effect of p-n heterojunction and modification of C-dots that facilitates the separation and transfer of electron-holes. Meanwhile, the modification of C-dots improves the harvesting of long wavelength solar light of photocatalysts due to its unique up-conversion photoluminescence (UCPL) characteristics. Eventually, the possible photocatalytic degradation path of the catalyst was inferred by LC-MS spectra, and the degradation mechanism was analyzed. This study sheds light on new possibilities for the application of photocatalysts in various light sources and has broad application prospects in water treatment.

Mechanism of Removal of Hexavalent Chromium from Aqueous Solution by Fe-Modified Biochar and Its Application

This study discussed the mechanism of Fe-modified biochar (FeBC) derived from rice straw biochar (BC) as an adsorbent for removing Cr(VI) from aqueous solution and assessed its applicability in actual industrial wastewater. The Cr(VI) removal percentage increased with the FeBC dose, which achieved a removal of 99.5% at 8.0 g/L FeBC. Increasing the solution pH from 2 to 10 slightly reduced Cr(VI) adsorption by 6.6%. Coexisting ions such as Ca2+, Na+ and Cl− inhibited the removal of Cr(VI); the removal rate decreased to 60% at their concentration of 0.25 mol/L. The adsorption isotherm and kinetics were better described by the Langmuir isotherm and pseudo-second-order kinetic models, respectively. Through scanning electron microscopy with energy dispersive X-ray, the Brunauer–Emmett–Teller method, Fourier transform infrared, X-ray diffraction and X-ray photoelectron spectroscopy, the analysis revealed that FeBC with iron oxides loaded onto its surface had more active sites than BC; the surface functional groups changed; the removal of Cr(VI) by FeBC was mainly attributed to electrostatic adsorption; the redox reaction of Cr, and Fe loaded onto BC enhanced Cr(VI) reduction process. FeBC showed a good removal performance on actual industrial wastewater with the concentration of both total Cr and Cr(VI) meeting the integrated wastewater discharge standard of China.

p-Cu2O/n-ZnO heterojunction thin films with enhanced photoelectrochemical properties and photocatalytic activities for norfloxacin

A two-step electrochemical deposition technique was applied to fabricate p-Cu₂O/n-ZnO heterojunction thin films. The influence of the deposition potential upon photoelectric performance of the prepared samples was examined utilizing XRD, XPS, SEM, UV-Vis, and electrochemical tests. The results show that the deposition potential has a substantial influence on the properties of the prepared samples. When the deposition potential is -0.45 V, the peak intensity of the (111) crystal plane of the prepared heterojunction is the highest, the band gap increased, and the morphology changes obviously compared to those of Cu₂O. The transient photocurrent value is three times that of pure Cu₂O, and the charge transfer resistance significantly reduced. The p-Cu₂O/n-ZnO heterojunction has a high carrier concentration. Photocatalytic degradation experiments show that degradation rate of norfloxacin increases by 14.4%-76.6%. The enhanced photocatalytic performance of Cu₂O is mainly due to the formation of a high-quality heterojunction and the change in the energy band structure, which promotes the transfer rate of the carrier and the separation of photogenic electron hole pairs, thus effectively improving the catalytic efficiency of photocatalysts. Active species detection experiments reveal that positive hole and superoxide anion radical play leading roles in norfloxacin molecule decomposition. In addition, a possible mechanism for the photocatalytic performance of p-Cu₂O enhanced by n-ZnO is proposed according to the analysis of the bandgap of p-Cu₂O and n-ZnO, along with the built-in electric field formed in the p-n heterojunction. This study provides an effective and alternative method for removing norfloxacin residues in wastewater.

Adsorption-photocatalysis synergistic removal of contaminants under antibiotic and Cr(VI) coexistence environment using non-metal g-C3N4 based nanomaterial obtained by supramolecular self-assembly method

Due to the rapid development of modern industry, the coexistence of antibiotics and inorganic heavy metals pollutants in wastewater has become a universal phenomenon. Therefore, developing efficient and eco-friendly photocatalyst for mixed pollutants degradation is significant. In this work, a well-designed phosphorus and sulfur co-doped g-C₃N₄ with feeble N vacancies catalyst (P/S-g-C₃N_x) was fabricated by supramolecular self-assembly method, and was applied to remove berberine hydrochloride (BH) and Cr(VI) simultaneously with the synergy of adsorption-photocatalysis. A series of experiments was conducted to unveil the synergistic mechanism. The kinetic models indicated that the adsorption of P/S-g-C₃N_x improved the BH removal process by accelerating the photo-degradation, because the adsorption rate > surface degradation rate > bulk degradation rate. Besides, the photo-degradation process improved the BH removal rate by regenerating the adsorption sites of P/S-g-C₃N_x. Moreover, from the experiments in BH-Cr(VI) mixed solution system, the existence of BH also enhanced the surface adsorption of Cr(VI) in P/S-g-C₃N_x sample, and the reduction rate of Cr(VI) was also promoted with the existence of BH. Overall, the results of this investigation suggest that the adsorption-photocatalysis synergy method is an efficient way to eliminate organic pollutant and Cr(VI) simultaneously.

Simple fabrication and unprecedented visible light response of NiNb2O6/RGO heterojunctions for the degradation of emerging pollutants in water

Utilization of environmentally friendly and effective synthesis methods to fabricate visible light responsive photocatalysts with impressive catalytic performance is desirable in photocatalytic water treatment.

Chitosan-MnO2 nanocomposite for effective removal of Cr (VI) from aqueous solution

In this report, the adsorption of Cr(VI) onto MnO₂/CS nanocomposite material from aqueous solution is investigated. All the factors, which affect the adsorption, such as pH, adsorption time, Cr(VI) initial concentration and adsorbent dosage, are also examined. The results obtained show that the Cr(VI) uptake is strongly affected by pH and ion strength. Analysis within the nonlinear isotherm models indicates that the Sips isotherm combining with the Langmuir and Freundlich models offer the best fit to the experimental data due to the obtained highest R² and smallest RMSE and χ² values. The calculated Langmuir monolayer adsorption capacity is 61.56 mg g^-1 at pH of 2.0 and adsorption time of 120 min. Moreover, the mechanism studies by combining theoretical models with analytical spectroscopies reveal that the electrostatic attraction plays the important role to the uptake of Cr(VI) onto MnO₂/CS nanocomposite. Therefore, the present nanocomposite material can be applied to remove total Cr from wastewater produced by the galvanized manufacturing factory with a relatively high efficiency.

Current Trends in the Application of Nanomaterials for the Removal of Emerging Micropollutants and Pathogens from Water

Water resources contamination has a worldwide impact and is a cause of global concern. The need for provision of clean water is becoming more and more demanding. Nanotechnology may support effective strategies for the treatment, use and reuse of water and the development of next-generation water supply systems. The excellent properties and effectiveness of nanomaterials make them particularly suitable for water/wastewater treatment. This review provides a comprehensive overview of the main categories of nanomaterials used in catalytic processes (carbon nanotubes/graphitic carbon nitride (CNT/g-C₃N₄) composites/graphene-based composites, metal oxides and composites, metal–organic framework and commercially available nanomaterials). These materials have found application in the removal of different categories of pollutants, including pharmaceutically active compounds, personal care products, organic micropollutants, as well as for the disinfection of bacterial, viral and protozoa microbial targets, in water and wastewater matrices. Apart from reviewing the characteristics and efficacy of the aforementioned nanoengineered materials for the removal of different pollutants, we have also recorded performance limitations issues (e.g., toxicity, operating conditions and reuse) for their practical application in water and wastewater treatment on large scale. Research efforts and continuous production are expected to support the development of eco-friendly, economic and efficient nanomaterials for real life applications in the near future.

Immobilized Ag3PO4/GO on 3D nickel foam and its photocatalytic degradation of norfloxacin antibiotic under visible light

In this study, a series of Ag₃PO₄/graphene oxide (GO) films were dip-coated on a metal nickel foam. The immobilized catalysts were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, Raman spectroscopy, high-resolution transmission electron microscopy and photoluminescence spectroscopy. The results show that Ag₃PO₄/GO was successfully supported on a nickel foam. The photocatalytic activity of the film catalyst under visible light was investigated by the degradation of norfloxacin, an antibiotic. Photocatalytic stability of this catalyst was also investigated. An optimized film exhibited superior activity and stability, the degradation rate of norfloxacin was about 83.68% in 100 min and the reaction rate constant k was 1.9 times that of pristine Ag₃PO₄. Further investigation found that photo-generated holes (h⁺) and superoxide anion radicals (·O₂⁻) are the main active species in the photodegradation process. The result indicates that the addition of GO inhibits the recombination of photogenerated electron–hole pairs, and thus has improved the photocatalytic activity and cyclic stability under visible light. The photocatalytic mechanism of the film catalyst was proposed. The prepared Ag₃PO₄/GO film catalyst is a promising candidate for treatment of wastewater containing antibiotics.

A series of Ag₃PO₄/graphene oxide catalysts were dip-coated onto 3D nickel foam for photocatalytic degradation of norfloxacin antibiotics.

Effect of reduced graphene oxide doping on photocatalytic reduction of Cr(VI) and photocatalytic oxidation of tetracycline by ZnAlTi layered double oxides under visible light

The existence of Cr(VI) and antibiotics in the environment can form the joint contaminant which can be hazardous to the ecosystem. To deal with this, we have explored a plausible method to remove the Cr(VI) and tetracycline (TC) from water by visible light photocatalysis. In this study, a series of reduced graphene oxide@ZnAlTi layered double oxides (rGO@LDO) composites with different doping ratio of rGO were successfully synthesized, which were applied in photocatalytic reduction of Cr(VI) and oxidation of TC. Graphene acts as an electron donor and it can enhance the adsorption of Cr(VI) and TC on the surface of the composites. It's found that the obtained ZnAlTi-LDO composites doped with rGO have higher photo-responsiveness in the visible region. The best-performing rGO@LDO composite (i.e., CGL3) exhibited enhanced visible light-driven photocatalytic Cr(VI) reduction, which was about five times higher than those of ZnAlTi-LDO (without adding hole catcher). The rGO@LDO also showed a satisfactory performance for photocatalytic oxidation of TC with the total organic carbon removal of 80%. However, the doping of rGO did not significantly enhance the removal of TC. The experiment of pH effects demonstrated that acidic pH was favorable to photocatalytic reduction of Cr(VI), while neutral pH was favorable to photocatalytic oxidation of TC. The band structure of ZnAlTi-LDO was first identified, and the E_VB and E_CB of ZnAlTi-LDO are -2.32 and 0.72 V (vs. RHE). This research provides a feasible method to remove Cr(VI) and tetracycline from water by employing ZnAlTi-LDO doped with rGO as photocatalyst.

The Roles of Nanomaterials in Conventional and Emerging Technologies for Heavy Metal Removal: A State-of-the-Art Review

Heavy metal (HM) pollution in waterways is a serious threat towards global water security, as high dosages of HM poisoning can significantly harm all living organisms. Researchers have developed promising methods to isolate, separate, or reduce these HMs from water bodies to overcome this. This includes techniques, such as adsorption, photocatalysis, and membrane removal. Nanomaterials play an integral role in all of these remediation techniques. Nanomaterials of different shapes have been atomically designed via various synthesis techniques, such as hydrothermal, wet chemical synthesis, and so on to develop unique nanomaterials with exceptional properties, including high surface area and porosity, modified surface charge, increment in active sites, enhanced photocatalytic efficiency, and improved HM removal selectivity. In this work, a comprehensive review on the role that nanomaterials play in removing HM from waterways. The unique characteristics of the nanomaterials, synthesis technique, and removal principles are presented. A detailed visualisation of HM removal performances and the mechanisms behind this improvement is also detailed. Finally, the future directions for the development of nanomaterials are highlighted.

Heterojunction Cu2O/RGO/BiVO4 ternary nanocomposites with enhanced photocatalytic activities towards degradation of rhodamine B and tetracycline hydrochloride

The synergy of BVO, Cu₂O and RGO inhibits the recombination of photogenic carriers to enhance the photocatalytic activity.