Photocatalytic reduction of Cr(VI) via surface modified g-C3N4 by acid-base regulation

Cr(VI) is a class of highly toxic heavy metals. In this study, alkali-modified g-C₃N₄ (cOH-CN) and acid-modified g-C₃N₄ (cH-CN) materials were successfully synthesized, and their photocatalytic activities for Cr(VI) reduction under visible light irradiation were tested. Owing to defect structures by cH-CN and -OH group introduction by cOH-CN, the modified materials exhibited a larger surface area, more abundant pore structures, a wider visible light absorption range, higher energy gap values, and a stronger capacity for electron-hole pair separation. As a result, satisfactory Cr(VI) reduction performance was gained by these two photocatalysts. Almost all Cr(VI) was converted to Cr(III) after 60 min of treatment in the presence of these two catalysts, while it was only 30% for the pristine g-C₃N₄ materials. Relatively higher dosages of cH-CN and cOH-CN and acidic conditions both improved Cr(VI) reduction in the cH-CN and cOH-CN photocatalytic systems. Cr(VI) reduction was mainly initiated by free electrons in the photocatalytic system of the modified materials. Finally, Cr(VI) in the photocatalytic system was almost completely converted to Cr(III). Furthermore, the stability and recycling of the cH-CN and cOH-CN catalysts were evaluated.

Ag-TiO2/biofilm/nitrate interface enhanced visible light-assisted biodegradation of tetracycline: The key role of nitrate as the electron accepter

Due to the pivotal role of Ag-TiO₂/biofilm/nitrate interface, enhanced visible light-assisted biodegradation of tetracycline (TC) in anoxic system was realized through both batch experiment and long-term operation in this study. The results of the batch experiment elucidated that 50 mg L^-1 TC could be completely removed within 10 h in Ag-TiO₂/biofilm/nitrate system. The continuous flow experiment was operated for 75 d to evaluate the performance and stability of Ag-TiO₂/biofilm/nitrate system. TC removal efficiency in Ag-TiO₂/biofilm/nitrate system was as high as 92.4 ± 1.6% at influent TC concentration of 50 mg L^-1 TC and hydraulic retention time (HRT) of 10 h, which would be attributed to the promoted separation of photoholes and photoelectrons at the presence of nitrate as electron acceptor. Facilitated electron transfer between semiconductor and biofilm was beneficial for enhancing TC biodegradation, thus lowering toxicity of intermediate products and promoting microbial activity. Moreover, the species related to TC biodegradation (Rhodopseudomonas, Phreatobacter and Stenotrophomonas), denitrification (Thauera) and electron transfer (Delftia) were enriched at Ag-TiO₂/biofilm/nitrate interface. Besides, a possible mechanism involved in enhanced TC degradation and nitrogen removal at Ag-TiO₂/biofilm/nitrate interface was proposed. This study provided a novel and promising strategy to enhance recalcitrant TC removal from industrial wastewater.

Magnetically modified in-situ N-doped Enteromorpha prolifera derived biochar for peroxydisulfate activation: Electron transfer induced singlet oxygen non-radical pathway

Herein, in-situ N-doped Enteromorpha prolifera derived magnetic biochar (MBC) was prepared by loading Fe₃O₄. It can effectively activate peroxodisulfate (PDS) to degrade tetracycline (TC) and easy recycling. The removal rate of TC reached 87.2%, and its possible degradation pathway was revealed through a liquid chromatography-mass spectrometer. This work first proposes the mechanism of in-situ N-doping and Fe synergistic effect on PDS activation. Unlike the well-reported role of N doping in activating PDS, except for the edge pyridine N plays a significant role in the activation of PDS. After the load of Fe, the synergistic effect of Fe and graphite N induces a non-radical path dominated by singlet oxygen (¹O₂) due to the excellent electron transfer function. Through chemical quenching experiment, electron spin detection, and electrochemical analysis, the mechanism of PDS activation by MBC was thoroughly investigate. This research will deepen the understanding of the mechanism of transition metals and carbon materials in synergistically driving PDS activation, and guide biochar-mediated PDS activation in environmental remediation.

Fabrication, characterization, and application of ternary magnetic recyclable Bi2WO6/BiOI@Fe3O4 composite for photodegradation of tetracycline in aqueous solutions

We aim at fabricating a ternary magnetic recyclable Bi₂WO₆/BiOI@Fe₃O₄ composite that could be applied for photodegradation of tetracycline (TC) from synthetic wastewater. To identify any changes with respect to the composite's morphology and crystal structure properties, ΧRD, FTIR, FESEM-EDS, PL and VSM analyses are carried out. The effects of Fe₃O₄ loading ratio on the Bi₂WO₆/BiOI for TC photodegradation are evaluated, while operational parameters such as pH, reaction time, TC concentration, and photocatalyst's dose are optimized. Removal mechanisms of the TC by the composite and its photodegradation pathways are elaborated. With respect to its performance, under the same optimized conditions (1 g/L of dose; 5 mg/L of TC; pH 7; 3 h of reaction time), the Bi₂WO₆/BiOI@5%Fe₃O₄ composite has the highest TC removal (97%), as compared to the Bi₂WO₆ (63%). After being saturated, the spent photocatalyst could be magnetically separated from solution for subsequent use. In spite of three consecutive cycles with 71% of efficiency, the spent composite still has reasonable photocatalytic activities for reuse. Overall, this suggests that the composite is a promising photocatalyst for TC removal from aqueous solutions.

Al cluster oxide modified a hematite/P3HT ternary Z-scheme photocatalyst with excellent photocatalytic performance: A discussion of the mechanism

The Z-scheme photocatalyst is valuable for use in polluted water purification, and there is a need to develop a cheap and efficient photocatalyst. This study presents a new type of Z-scheme photocatalytic material composed of hematite and P3HT, also, the Al cluster oxides were first used as a charge transfer mediator to construct Z-scheme photocatalysis system. In addition, by analyzing the electron rearrangement phenomenon exhibited by the XPS spectrum and the experimental results of the in-situ illumination XPS, it is found that Al cluster is beneficial to the electron multi-step charge transfer process and Al cluster favors the construction of Z-scheme structure between hematite and P3HT. This Poly-3-hexylthiophene (P3HT)/Al cluster oxide/hematite ternary photocatalyst exhibited an excellent degradation effect on bisphenol A and tetracycline. This study demonstrates the feasibility of using the Al cluster as a charge mediator in the Z-scheme, providing new Z-scheme catalyst construction idea which is beneficial to the popularization and use of Z-scheme system in practical applications, and providing a new material for water pollution purification.

A novel immobilized Z-scheme P3HT/α-Fe2O3 photocatalyst array: Study on the excellent photocatalytic performance and photocatalytic mechanism

The Z-scheme photocatalyst is valuable for use in polluted water purification. To improve the practical application value of the Z-scheme, in this study, a nano α-Fe₂O₃ and P3HT composite photocatalyst array was synthesized by electrophoretic deposition for the first time. This material was named F1P. The EPR, VBXPS and in situ illumination XPS analyses indicated that the charge transfer path of F1P conforms to the Z-scheme, and F1P array has a high light energy conversion efficiency. Due to the advantages of the Z-scheme system and the good light harvesting ability, F1P exhibited a good degradation effect on different types of pollutants under visible light irradiation. The degradation efficiency of tetracycline and bisphenol A by F1P can reach 97 % and 99 %, respectively. Moreover, F1P showed a certain resistance to water quality changes. After four cycles, F1P can maintain the structural stability and good pollutant treatment effect. Due to the high redox ability of F1P, the complex structure of pollutants can be destroyed and the degradation path of pollutants in F1P system was also analyzed. This study provides a new way of synthesizing Z-scheme systems and immobilizing Z-scheme photocatalysts. F1P is a new material with high practicability.

Nitrogen deficient carbon nitride for efficient visible light driven tetracycline degradation: a combination of experimental and DFT studies

The narrow visible-light absorption range and a high recombination rate of photo-excited electrons and holes are the main reasons for the confined photocatalytic performance of graphitic carbon nitride (g-C₃N₄).

Synthesis of a Novel Catalyst MnO/CNTs for Microwave-Induced Degradation of Tetracycline

Microwave-induced catalytic degradation (MICD) has been considered as one of the most prospective approaches to remove organic contaminants from water. High-performance catalysts, ideally offering efficient degradation ability, are essential to this process. This work reports the fabrication of manganese oxide on carbon nanotubes (MnO/CNTs) as an efficient catalyst under microwave irradiation (MI) to remove tetracycline (TC) from aqueous solution. The hybrid MnO/CNTs structure shows excellent performance in TC degradation. Combining experimental characterization and theoretical calculations, synergistic mechanisms are revealed: (i) Strong MnO/CNTs interaction stabilizes Mn(II) through interfacial bonding; (ii) high-spin states associated with low coordinated Mn(II) play a major role in MICD; and (iii) superoxide radicals (•O2−) and hydroxyl radicals (•OH) induced by microwave input are identified as the major active species.

Polypyrrole/cadmium sulfide hollow fiber with high performance contaminant removal and photocatalytic activity fabricated by layer-by-layer deposition and fiber-sacrifice template approach

A recyclable polypyrrole (PPy)/cadmium sulfide (CdS) hollow fiber photocatalyst was innovatively fabricated for solving the loss issue of the current powder-form photocatalyst in slurry system. Core-sheath structure CdS/polyacrylonitrile (PAN) fiber was prepared via successive ionic layer adsorption and reaction (SILAR) method on the surface of PAN fiber. PPy was further deposited on the CdS/PAN fiber by vapor deposition polymerization. After the removal of interior PAN template, PPy/CdS hollow fiber was yielded. The hollow structure of PPy/CdS hollow fiber was confirmed by morphology observation. The resulting PPy/CdS hollow fiber presents low energy band gaps of 1.9 eV, which accounts for enhanced visible light photocatalytic activity after PPy deposition. PPy/CdS hollow fiber shows good dye removal efficiency of 73.06 wt% (dosage of the product as low as 5 mg·10 mL^-1), and praiseworthy H₂ production rate up to 269.7 μmol·g^-1·h^-1. PPy/CdS hollow fiber maintained high and sustainable photocatalytic activity compared to CdS/PAN fiber after 8 cycles, indicating that PPy effectively improved the stability of CdS. Here, PPy plays key synergistic role in photocatalysis of PPy/CdS hollow fiber for the promotive and protective effects based on the actual photocatalytic performance and inductively coupled plasma optical emission spectrometer (ICP-OES) results. Compared with nano-sized photocatalysts, the fiber-formed PPy/CdS hollow fiber is highly bulky and easy to recycle. PPy/CdS hollow fiber has great potential for scale-up in industrial application because of its excellent grabbing ability and degradation to contaminants, and ease of disposal.

Efficient photocatalytic reactions of Cr(vi) reduction and ciprofloxacin and RhB oxidation with Sn(ii)-doped BiOBr

Efficient photocatalytic reactions of Cr(VI) reduction, ciprofloxacin and RhB oxidation with Sn(II) doped BiOBr.

Enhanced selectivity for photodegrading ciprofloxacin by a magnetic photocatalyst modified with a POPD–CdS heterojunction embedded imprinted layer

A POPD–CdS heterojunction embedded magnetic imprinted photocatalyst achieves the purpose of selective photodegradation of ciprofloxacin and effectively suppresses the secondary pollution caused by CdS photocorrosion.

Three-dimensional bandgap-tuned Ag2S quantum dots/reduced graphene oxide composites with enhanced adsorption and photocatalysis under visible light

Tuning Ag₂S bandgap by quantum size effect and incorporation with rGO to form a three-dimensional composite enhances adsorption and photocatalysis under visible-light.

Construction of stable core–shell imprinted Ag-(poly-o-phenylenediamine)/CoFe2O4 photocatalyst endowed with the specific recognition capability for selective photodegradation of ciprofloxacin

The stable core–shell imprinted Ag-POPD/CoFe₂O₄ photocatalyst not only possessed high photocatalytic activity, but also exhibited the superior specific recognition capability for selective photodegradation of CIP.