Construction of BiOIO3/AgIO3 Z-Scheme Photocatalysts for the Efficient Removal of Persistent Organic Pollutants under Natural Sunlight Illumination

Bimetallic Au/Ag coated on In2O3 for the effective removal of emerging organic contaminants under natural sunlight irradiation

Antibiotics-polluted wastewater, likely causing the spread of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs), can be effectively remediated by photocatalytic degradation driven by endless solar energy. Herein, bimetallic Au/Ag is deposited on In2O3 surface via a one-step sintering process followed by a controllable chemical reduction approach. Under natural sunlight irradiation, the optimal Au/Ag/In2O3 (UGI-1.0) photocatalyst possesses a considerable norfloxacin (NOR) degradation rate constant of 0.013 min-1, which is 3.25, 1.63, and 1.86 times higher than that of In2O3, Ag/In2O3, and Au/In2O3 respectively. The effect of many water characteristics (e.g., humic acid, water bodies, pH values, and coexisting anions) on the photodegradation performance of NOR over UGI-1.0 is investigated. Moreover, other persistent organic pollutants (ofloxacin, phenol, 2,4-dichlorophenol, and rhodamine B) can also be degraded over UGI-1.0, suggesting its universal oxidation capacity. To settle the challenge of powder photocatalyst recovery, the UGI-1.0 photocatalyst is coated on a frosted glass sheet, which exhibits outstanding activity and stability for degrading NOR. The bimetallic Au/Ag deposited on In2O3 promote its photo-absorption, and enhance its photoinduced charge separation and transfer efficiency by serving as electron accepter, leading to the boosted activity of Au/Ag/In2O3 catalysts. Particularly, the cultivation of staphylococcus aureus (S. aureus) and cabbage seeds reveals the efficient toxicity reduction of NOR by photocatalytic degradation and the nontoxic characteristic of UGI-1.0 catalyst. This work unveils the feasibility of UGI-1.0 to remediate real wastewater with the assistance of solar energy.

Tuning the Charge Transfer in MWCNTs via the Incorporation of ZnONPs and AgNPs: The Role of Carbon Binding with ZnO/Ag Heterostructures in Reactive Species Formation

In this research, multi-walled carbon nanotubes (MWCNTs) were decorated with two kinds of nanostructures, (1) silver nanoparticles (AgNPs) and (2) zinc oxide-silver nano-heterostructures (ZnO/Ag-NHs), via an accessible chemical coprecipitation method assisted with ultrasonic radiation. The high-resolution transmission electron microscopy analysis demonstrated the successful decoration of MWCNTs with the nanostructures with a diameter size of 11 nm ± 2 nm and 46 nm ± 5 nm for the AgNPs and the ZnO/Ag-NHs, respectively. The reactive species were promoted in an aqueous medium assisted with UV irradiation on the functionalized MWCNT. UV-Vis spectroscopy demonstrated that production of the reactive species density increased 4.07 times, promoted by the single MWCNT after the functionalization. X-ray photoelectron spectroscopy showed that Sp2 hybridization in carbon atoms of MWCNTs participates in the binding of AgNPs and ZnO/Ag-NH decoration and thus participates in the formation of reactive species in an aqueous medium, as is the case for cancer cells.

Modulating Surface-Adsorbed Oxygen Species of Bismuth Silicate by a Solid Solution Strategy for Efficient Adsorption and Photocatalytic Activity

Bismuth silicate photocatalysts suffer from insufficient photocatalytic activity due to an insufficient number of surface active sites and low carrier separation and transport efficiency, which can be solved by defect modulation. Herein, Bi12SiO20/Bi2O2SiO3-BiOClxBr1-x (BSOCB) photocatalysts with a high concentration of surface-adsorbed oxygen species (SAOS) are synthesized by introducing a BiOClxBr1-x solid solution to modify nonhomogeneous BSO via an ion exchange strategy. The introduction of a solid solution enables the generation of dispersed nanoflowers and the regulation of SAOS due to the fact that anion-cation copolymerization guides the crystal growth, and the defects generated by the lattice distortion modulate the concentration of SAOS on the catalysts during the solid solution process. The obtained typical BSOCB photocatalyst possesses both high adsorption and photocatalytic properties, and the results show that it not only can almost completely degrade the traditional pollutant RhB within 20 min but also strongly degrades antibiotics, such as CIP (light for 150 min, 96%), NFX (light for 150 min, 87%), and TC (light for 150 min, 77%). This work provides a new approach for obtaining bismuth-based photocatalysts with controllable morphology and a large number of surface active sites and provides a theoretical and experimental basis for expanding the application scenarios of photocatalysts.

Wastewater Treatment Using High-Performance In Situ Formed Double-Heterojunction Janus Photocatalyst Microparticles Shaped via a Microfluidic Device

In this work, a heterogeneous photocatalysis system is fabricated for treating wastewater containing organic dyes and pharmaceutical substances. Double-heterojunction Janus photocatalysts are formed on the surface of size-tunable polydimethylsiloxane (PDMS) microparticles shaped via simple and low-cost coflow microfluidic devices. Ag0/Ag0-TiO2/TiO2 Janus-like photocatalysts are synthesized on the surface of porous PDMS microparticles as the support in which the metal-semiconductor heterojunction of Ag0/Ag0-TiO2 and the second heterojunction of Ag0-TiO2/TiO2 are created in situ, leading to the formation of Ag0/Ag0-TiO2/TiO2@PDMS photocatalysis systems. To form the heterojunctions on the PDMS surface, the polymer chain etching method is employed as a desired strategy to have half of the TiO2 nanoparticles on the surface of microparticles, which are treated by a Ag source. Using salt additives and the etching method, PDMS microparticles are made porous, providing more surface area for photoreactions. Surprisingly, the highest decomposition efficiencies of 94.4 and 91.1% are achieved for rhodamine B(RhB) and tetracycline (TC), respectively, under visible light for 60 min pH 11, a light source at a distance of 2 cm, 5 mM AgNO3, 10 wt % TiO2, 7 wt % NaCl, and 20 gm/L photocatalyst, which are conditions that result in the best performance for RhB degradation. Regarding the stability of the photocatalysts, no significant change is observed in the performance after five cycles.

Oxygen-deficient AgIO3 for efficiently photodegrading organic contaminants under natural sunlight

Defect engineering is regarded as an effective strategy to boost the photo-activity of photocatalysts for organic contaminants removal. In this work, abundant surface oxygen vacancies (Ov) are created on AgIO3 microsheets (AgIO3-OV) by a facile and controllable hydrogen chemical reduction approach. The introduction of surface Ov on AgIO3 broadens the photo-absorption region from ultraviolet to visible light, accelerates the photoinduced charges separation and migration, and also activates the formation of superoxide radicals (•O2-). The AgIO3-OV possesses an outstanding degradation rate constant of 0.035 min-1, for photocatalytic degrading methyl orange (MO) under illumination of natural sunlight with a light intensity is 50 mW/cm2, which is 7 and 3.5 times that of the pristine AgIO3 and C-AgIO3 (AgIO3 is calcined in air without generating Ov). In addition, the AgIO3-OV also exhibit considerable photoactivity for degrading other diverse organic contaminants, including azo dye (rhodamine B (RhB)), antibiotics (sulflsoxazole (SOX), norfloxacin (NOR), chlortetracycline hydrochloride (CTC), tetracycline hydrochloride (TC) and ofloxacin (OFX)), and even the mixture of organic contaminants (MO-RhB and CTC-OFX). After natural sunlight illumination for 50 min, 41.4% of total organic carbon (TOC) for MO-RhB mixed solution can be decreased over AgIO3-OV. In a broad range of solution pH from 3 to 11 or diverse water bodies of MO solution, AgIO3-OV exhibits attractive activity for decomposing MO. The MO photo-degradation process and mechanism over AgIO3-OV under natural sunlight irradiation has been systemically investigated and proposed. The toxicities of MO and its degradation intermediates over AgIO3-OV are compared using Toxicity Estimation Software (T.E.S.T.). Moreover, the non-toxicity of both AgIO3-OV catalyst and treated antibiotic solution (CTC-OFX mixture) are confirmed by E. coli DH5a cultivation test, supporting the feasibility of AgIO3-OV catalyst to treat organic contaminants in real water under natural sunlight illumination.

Boosting the activity for organic pollutants removal of In2O3 by loading Ag particles under natural sunlight irradiation

A novel photocatalyst In2O3 with loading Ag particles is prepared via a facile one-step annealing method in air atmosphere. The Ag/In2O3 exhibits considerable photoactivity for decomposing sulfisoxazole (SOX), tetracycline hydrochloride (TC), and rhodamine B (RhB) under natural sunlight irradiation, which is much higher than that of pristine In2O3 and Ag species. After natural sunlight irradiation for 100 min, 70.6% of SOX, 65.6% of TC, and 81.9% of RhB are degraded over Ag/In2O3, and their corresponding chemical oxygen demand (COD) removal ratio achieve 95.4%, 38.4%, and 93.6%, respectively. A batch of experiments for degrading SOX with adjusting pollutant solution pH and adding coexisting anions over Ag/In2O3 are carried out to estimate its practical application prospect. Particularly, the as-prepared Ag/In2O3 possesses a superior stability, which exhibits no noticeable deactivation in decomposing SOX after eight cycles' reactions. In addition, the Ag/In2O3 coated on a frosted glass plate, also possesses a superior activity and stability for SOX removal, which solve the possible second pollution of residual powdered catalyst in water. Ag particles on In2O3 working as electron accepter improve charge separation and transfer efficiency, as well as the photo-absorption and organic pollutants affinity, leading to the boosted photoactivity of Ag/In2O3. The photocatalytic mechanism for degrading SOX and degradation process over Ag/In2O3 has been systemically investigated and proposed. This work offers an archetype for the rational design of highly efficient photocatalysts by metal loading.

Synergistic effect of Fe doping and oxygen vacancy in AgIO3 for effectively degrading organic pollutants under natural sunlight

In this work, a series of hydrogenated Fe-doped AgIO3 (FAI-x) catalysts are synthesized for photodegrading diverse azo dyes and antibiotics. Under the irradiation of natural sunlight with a light intensity of ∼60 mW/cm2, the optimum FAI-10 exhibits a considerable rate constant for decomposing methyl orange (MO) of 0.067 min-1, about 7.4 times higher than that of AgIO3 (0.009 min-1), and 24.6% and 83.8% of MO can be decomposed over AgIO3 and FAI-10 after irradiation for 40 min. In the amplification photodegradation experiments with using 0.5 g catalyst and 400 mL MO dye solution (10 mg/L), FAI-10 possesses greatly higher photoreactivity to common semiconductors (ZnO, TiO2, In2O3 and Bi2MoO6), and the photodegradation rates over FAI-10 are 92%. Particularly, the FAI-10 shows superior stability, the activity of which remains unaltered after 8 continuous cycles. Foreign ions and water bodies have slight effect on the activity of FAI-10, but the MO degradation rates are decreased by adjusting pH values, especially when pH = 11 because of the strong electrostatic repulsion between MO and FAI-10. FAI-10 can also effectively decompose another azo dye (rhodamine B (RhB)) and diverse antibiotics (sulflsoxazole (SOX), chlortetracycline hydrochloride (CTC), tetracycline hydrochloride (TC) and ofloxacin (OFX)). The activity enhancement mechanism of FAI-10 has been systemically investigated and is ascribed to the promoted photo-absorption, charge separation and transfer efficiency, and affinity of organic pollutants, owing to the synergistic effect of Fe doping and oxygen vacancy (Ov). The photocatalytic mechanisms and process for decomposing MO are verified and proposed based on radical trapping experiments and liquid chromatography-mass spectrometry (LC-MS). This work opens an avenue for the fabrication of effective photocatalysts toward water purification.

Pd@Bi2Ru2O7/BiVO4 Z-Scheme Heterojunction Nanocomposite Photocatalyst for the Degradation of Trichloroethylene

Photocatalytic degradation of chlorinated persistent organic pollutants is a very challenging process due to the high redox potential of the C-Cl bond that requires wide band gap catalysts that are activated under UV light. Designing a Z-scheme heterojunction between visible light-activated metal oxides with compatible band gaps enables these redox potentials. Herein, we report the design of a pyrochlore/Aurivillius Z-scheme heterojunction to enhance the photocatalytic activity of BiVO4 for the degradation of trichloroethylene. We prepared Bi2Ru2O7/BiVO4 heterostructured photocatalysts by a controlled hydrothermal approach. Upon optimizing the Bi2Ru2O7 ratio to 1.0 wt %, the heterostructured photocatalyst demonstrated enhanced activity in the degradation of trichloroethylene (TCE) under simulated sunlight irradiation compared to bare BiVO4 and Bi2Ru2O7, respectively. Decorating the surface of the catalyst with palladium nanodomains to create the Pd@Bi2Ru2O7/BiVO4 nanocomposite showed a substantial increase in the photocatalytic degradation of TCE. The material characterization indicated that the architecture of the material provides a synergy of enhancing the redox potential of the photocatalyst and improving the charge carrier dynamics. Furthermore, the photoelectrochemical characterization confirmed that the dual heterojunctions in the Pd@Bi2Ru2O7/BiVO4 nanocomposite resulted in improved interfacial charge carrier transfer and enhanced the electron/hole separation efficiency compared to the nonpalladized catalysts. This work provides a promising approach for band gap engineering of visible light photocatalysts for the degradation of halogenated persistent organic pollutants.

Cost-Effective and Highly Efficient Manganese-Doped MoS2 Nanosheets as Visible-Light-Driven Photocatalysts for Wastewater Treatment

One of the main objectives in wastewater treatment and sustainable energy production is to find photocatalysts that are favorably efficient and cost-effective. Transition-metal dichalcogenides (TMDs) are promising photocatalytic materials; out of all, MoS₂ is extensively studied as a cocatalyst in the TMD library due to its exceptional photocatalytic activity for the degradation of organic dyes due to its distinctive morphology, adequate optical absorption, and rich active sites. However, sulfur ions on the active edges facilitate the catalytic activity of MoS₂. On the basal planes, sulfur ions are catalytically inactive. Injecting metal atoms into the MoS₂ lattice is a handy approach for triggering the surface of the basal planes and enriching catalytically active sites. Effective band gap engineering, sulfur edges, and improved optical absorption of Mn-doped MoS₂ nanostructures are promising for improving their charge separation and photostimulated dye degradation activity. The percentage of dye degradation of MB under visible-light irradiations was found to be 89.87 and 100% for pristine and 20% Mn-doped MoS₂ in 150 and 90 min, respectively. However, the degradation of MB dye was increased when the doping concentration in MoS₂ increased from 5 to 20%. The kinetic study showed that the first-order kinetic model described the photodegradation mechanism well. After four cycles, the 20% Mn-doped MoS₂ catalysts maintained comparable catalytic efficacy, indicating its excellent stability. The results demonstrated that the Mn-doped MoS₂ nanostructures exhibit exceptional visible-light-driven photocatalytic activity and could perform well as a catalyst for industrial wastewater treatment.