Visible light photocatalytic activity enhancement and mechanism of AgBr/Ag3PO4 hybrids for degradation of methyl orange

Preparation of thiourea derivative incorporated Ag3PO4 core shell for enhancement of photocatalytic degradation performance of organic dye under visible radiation light

Photocatalysis is a promising technique to reduce hazardous organic pollutants using semiconductors under visible light. However, previous studies have been concerned with the behavior of silver phosphate (Ag3PO4) as n-type semiconductors, and the problem of their instability is still under investigation. Herein, 4,4'-(((oxalylbis(azanediyl)) bis(carbonothioyl)) bis(azanediyl)) dibenzoic acid is synthesized by green method and used to enhance the photocatalytic behavior for Ag3PO4. The incorporated Ag3PO4 core-shell is prepared and characterized via XRD, FT-IR, Raman, TEM and BET. Besides, the thermal stability of the prepared core shell was investigated via TGA and DSC measurements. The optical properties and the energy band gap are determined using photoluminescence and DRS measurements. The photodegradation of methylene blue in the presence of the synthesized Ag3PO4 core-shell under visible light is examined using UV/Vis measurements. The effect of initial dye concentration and contact time are studied. In addition, the kinetic behavior of the selected dye during the photodegradation process shows a pseudo-first order reaction with rate constant of 0.015 min-1 for ZAg. The reusability of the Ag3PO4 core shell is evaluated, and the efficiency changed from 96.76 to 94.02% after three cycles, indicating efficient photocatalytic behavior with excellent stability.

Cu2+1O/Ag Heterostructure for Boosting the Electrocatalytic Nitrate Reduction to Ammonia Performance

Electrocatalytic nitrate reduction reaction (ENO₃RR) is an alternative, sustainable, and environmentally friendly value-added NH₃ synthesis method under ambient conditions relative to the traditional Haber-Bosch process; however, its low NH₃ yield, low Faradaic efficiency (FE), low selectivity, and low conversion rate severely restrict the development. In this work, a Cu₂₊₁O/Ag-CC heterostructured electrocatalyst was successfully fabricated by constructing a heterogeneous interface between Cu₂₊₁O and Ag for selective electrochemical nitrate-to-ammonia conversion. The construction of the heterogeneous interface effectively promotes the synergistic effect of the catalytically active components Cu₂₊₁O and Ag, which enhances the material conductivity, accelerates the interfacial electron transfer, and exposes more active sites, thus improving the performance of ENO₃RR. Such Cu₂₊₁O/Ag-CC manifests a high NH₃ yield of 2.2 mg h^-1 cm^-2 and a notable ammonia FE of 85.03% at the optimal applied potential of -0.74 V vs RHE in a relatively low concentration of 0.01 M NO₃^--containing 0.1 M KOH. Moreover, it shows excellent electrochemical stability during the cycle tests. Our study not only provides an efficient catalyst for ammonia electro-synthesis from ENO₃RR but also an effective strategy for the construction of ENO₃RR electrocatalysts for electrocatalytic applications.

Recyclable Carbon Cloth-Supported ZnO@Ag3PO4 Core-Shell Structure for Photocatalytic Degradation of Organic Dye

The extensive use of organic dyes in industry has caused serious environmental problems, and photocatalysis is a potential solution to water pollution by organic dyes. The practical application of powdery photocatalysts is usually limited by the rapid recombination of charge carriers and difficulty in recycling. In this study, recyclable carbon cloth-supported ZnO@Ag₃PO₄ composite with a core-shell structure was successfully prepared by solvothermal treatment and subsequent impregnation-deposition. The as-prepared carbon cloth-supported ZnO@Ag₃PO₄ composite showed an improved photocatalytic activity and stability for the degradation of rhodamine B (RhB), a model organic dye, under visible light irradiation. The decomposition ratio of RhB reached 87.1% after exposure to visible light for 100 min, corresponding to a reaction rate constant that was 4.8 and 15.9 times that of carbon cloth-supported Ag₃PO₄ or ZnO alone. The enhanced performance of the composite can be attributed to the effectively inhibited recombination of photoinduced electron-hole pairs by the S-scheme heterojunction. The carbon fibers further promoted the transfer of charges. Moreover, the carbon cloth-supported ZnO@Ag₃PO₄ can be easily separated from the solution and repeatedly used, demonstrating a fair recyclability and potential in practical applications.

Perovskite LaNiO3/Ag3PO4 heterojunction photocatalyst for the degradation of dyes

Pristine lanthanum nickelate (LaNiO₃), silver phosphate (Ag₃PO₄) and perovskite lanthanum nickelate silver phosphate composites (LaNiO₃/Ag₃PO₄) were prepared using the facile hydrothermal method. Three composites were synthesized by varying the percentage of LaNiO₃ in Ag₃PO₄. The physical properties of as-prepared samples were studied by powder X-ray diffraction (pXRD), Fourier-transform infrared (FT-IR), Scanning electron microscopy (SEM) and Energy-dispersive X-ray (EDX). Among all synthesized photocatalysts, 5%LaNiO₃/Ag₃PO₄ composite has been proved to be an excellent visible light photocatalyst for the degradation of dyes i.e., rhodamine B (RhB) and methyl orange (MO). The photocatalytic activity and stability of Ag₃PO₄ were also enhanced by introducing LaNiO₃ in Ag₃PO₄ heterojunction formation. Complete photodegradation of 50 mg/L of RhB and MO solutions using 25 mg of 5%LaNiO₃/Ag₃PO₄ photocatalyst was observed in just 20 min. Photodegradation of RhB and MO using 5%LaNiO₃/Ag₃PO₄ catalyst follows first-order kinetics with rate constants of 0.213 and 0.1804 min^-1, respectively. Perovskite LaNiO₃/Ag₃PO₄ photocatalyst showed the highest stability up to five cycles. The photodegradation mechanism suggests that the holes ( h ⁺) and superoxide anion radicals O 2   • - plays a main role in the dye degradation of RhB and MO.

High-Efficient Visible-Light Photocatalysis Performance and Light-Corrosion Resistance of Ag3PO4 Constructed by double-Z System Composites

Novel visible-light-driven Ag₃PO₄/AgBr/AgI photocatalysts were prepared via a simple self-assembly strategy combined with in-situ anion-exchanging process. The photocatalytic activity of Ag₃PO₄ was significantly improved by constructing double-Z system. Specifically, the obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy (DRS). Under visible light irradiation (λ > 420 nm), the Ag₃PO₄/AgBr/AgI photocatalysts showed much higher photocatalytic activity than bulk Ag₃PO₄ for the degradation of formaldehyde (HCHO), and 100% HCHO degradation could be obtained within 28 min. The degradation efficiency could be maintained in five cycles. Further electron paramagnetic resonance (ESR) tests demonstrated that both •OH and •O₂^- generated in the system. This study provides new insights into the fabrication of highly efficient visible-light-driven photocatalysts and facilitates their practical application in emerging environment issues.

Construction of Z-scheme Ag-AgBr/Bi2O2CO3/CNT heterojunctions with remarkable photocatalytic performance using carbon nanotubes as efficient electronic mediators

It is a useful strategy to use a solid electronic mediator with good conductivity to assist the separation of semiconductor photo-induced electron-hole pairs and the redox of semiconductor materials. In order to construct a photocatalyst for more efficient photocatalytic degradation of antibiotics, a simple hydrothermal and precipitation method was used to construct the Ag-AgBr/Bi₂O₂CO₃/CNT Z-scheme heterojunction by using carbon nanotubes (CNTs) as electronic mediators. Compared with the pristine AgBr, Bi₂O₂CO₃, Bi₂O₂CO₃/CNT, the 30%Ag-AgBr/Bi₂O₂CO₃/CNT photocatalyst has better photocatalytic activity under visible light irradiation, showing the best degradation ability to tetracycline (TC). Meanwhile, the photocatalytic properties of 30%Ag-AgBr/Bi₂O₂CO₃/CNT in different pH and inorganic ions were studied. Finally, the degradation pathway and catalytic mechanism of 30%Ag-AgBr/Bi₂O₂CO₃/CNT photocatalytic degradation of TC were also argued. The construction of the Z-scheme electron transport pathway, in which CNTs were used as electronic mediators, and the SPR effect of Ag and Bi metal, which enable the effective separation and transfer of photo-generated electron-hole pairs, are responsible for the significant improvement in photocatalytic performance. It opens up new possibilities for designing and developing high-efficiency photocatalysts with CNTs as the electronic mediator.

Integration of biochar into Ag3PO4/α-Fe2O3 heterojunction for enhanced reactive oxygen species generation towards organic pollutants removal

A biochar (BC) harbored Ag₃PO₄/α-Fe₂O₃ type-Ⅰ heterojunction (Ag-Fe-BC) was prepared by a hydrothermal-impregnation method to transfer active center of heterojunctions. The electrochemical and spectroscopic tests demonstrated that BC enhanced the catalytic performance of the heterojunction by enhancing photocurrent, reducing fluorescence intensity, and facilitating separation of electron-hole pairs. The photocatalytic activity showed the Ag-Fe-BC (5:1:3) could degrade Rhodamine B (20 mg/L) by up to 92.7%, which was 3.35 times higher than Ag₃PO₄/α-Fe₂O₃. Tetracycline and ciprofloxacin (20 mg/L) were degraded efficiently by 58.3% and 79.4% within 2 h, respectively. Electron paramagnetic resonance and scavenging experiments confirmed the major reactive oxygen species (ROS) consisted of singlet oxygen (¹O₂) and superoxide (·O₂^-). Excellent RhB adsorption and electrons capturing capacity of BC facilitated electron-hole pairs separation and ROS transferring to target organics followed by elevated degradation. Thus, a facile method was proposed to synthesize a highly efficient visible-light responsive photocatalyst for degradation of various organics in water.

Enhanced photocatalytic treatment using plasmonic Ag@Ag3PO4/Ag@AgCl nanophotocatalyst for simultaneous degradation of multiple parabens and UV-filters in various aquatic environments under visible light irradiation

In this study, simultaneous photocatalytic degradation of different parabens (methyl-, ethyl-, propyl-, and butyl paraben) and UV filters (benzophenone-3, 4-methylbenzylidene camphor, 2-ethylhexyl 4-(dimethylamino) benzoate, ethylhexyl methoxycinnamate and octocrylene) in water matrices was performed under visible light irradiation using novel double plasmonic Ag^@Ag₃PO₄/Ag^@AgCl nanophotocatalyst, synthesized by an easy and fast photochemical conversion and photo-reduction. It was found that the nanophotocatalyst with appropriate mole ratio of Ag^@Ag₃PO₄/Ag^@AgCl (1:3) showed superior photocatalytic activity than individual plasmonic nanoparticles. This is because there are two simultaneous surface plasmon resonances (SPR) generated by the metallic Ag nanoparticles, in addition to the hetero-junction structure formed at the interface between Ag^@Ag₃PO₄ and Ag^@AgCl. The structures of the synthesized photocatalysts were characterized, and the principal reactive oxygen species in the photocatalytic process were identified via a trapping experiment, confirming superoxide radicals (^∙O₂^-) as the key reactive species of the photocatalytic system. The process of photodegradation of the target pollutants was monitored using an optimized method that incorporated solid-phase extraction in combination with gas chromatography-mass spectrometry. The simultaneous photodegradation process was modeled and optimized using central composite design. The kinetic study revealed that the degradation process over Ag^@Ag₃PO_{4 (30%)}/Ag^@AgCl _(70%) under visible light followed a pseudo-first-order kinetic model. The simultaneous degradation of target compounds was further investigated in sewage treatment plant effluent as well as tap water. It was found that the matrix constituents can reduce the photodegradation efficiency, especially in the case of highly contaminated samples.

Light-responsive polyurethanes: classification of light-responsive moieties, light-responsive reactions, and their applications

Stimuli responsiveness has been an attractive feature of smart material design, wherein the chemical and physical properties of the material can be varied in response to small environmental change. Polyurethane (PU), a widely used synthetic polymer can be upgraded into a light-responsive smart polymer by introducing a light-sensitive moiety into the polymer matrix. For instance, azobenzene, spiropyran, and coumarin result in reversible light-induced reactions, while o-nitrobenzyl can result in irreversible light-induced reactions. These variations of light-stimulus properties endow PU with wide ranges of physical, mechanical, and chemical changes upon exposure to different wavelengths of light. PU responsiveness has rarely been reviewed even though it is known to be one of the most versatile polymers with diverse ranges of applications in household, automotive, electronic, construction, medical, and biomedical industries. This review focuses on the classes of light-responsive moieties used in PU systems, their synthesis, and the response mechanism of light-responsive PU-based materials, which also include dual- or multi-responsive light-responsive PU systems. The advantages and limitations of light-responsive PU are reviewed and challenges in the development of light-responsive PU are discussed.

Cobalt-ferrite/Ag-fMWCNT hybrid nanocomposite catalyst for efficient degradation of synthetic organic dyes via peroxymonosulfate activation

The activation of peroxymonosulfate (PMS) by nanocatalysts has shown promise as an effective wastewater treatment protocol. Magnetic CoFe₂O₄/Ag-nanoparticles (NPs) anchored on functionalized multiwalled carbon nanotubes (fMWCNTs), a support material, were synthesized using a one-pot solvothermal method. The surface morphologies and physicochemical properties of the CoFe₂O₄/Ag-fMWCNT hybrid nanocomposite catalyst were investigated by powder X-ray diffraction analysis, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and nitrogen adsorption-desorption isotherms. The activity of the nanocomposite combined with PMS (serving as an activator) toward the degradation of rhodamine B, methylene blue, methyl orange, and methyl red was investigated. The obtained optimal 0.02 g CoFe₂O₄/Ag-fMWCNTs exhibited the highest PMS activation performance, with a removal percentage of 100% for 20 ppm dye concentration at pH 6.5 within 14 min. In addition, the rhodamine B degradation product was investigated by analyzing the intermediate products by liquid chromatography/mass spectrometry (LC-MS). The homogeneous distribution of CoFe₂O₄/Ag NPs on fMWCNTs accelerated PMS activation and enhanced the catalytic degradation of dyes. The effects of the reaction parameters on the dye degradation efficiency were investigated by using different nanocatalysts (fMWCNTs, CoFe₂O₄/fMWCNTs, and CoFe₂O₄/Ag-fMWCNTs) as well as by varying the pH (3-11), dye concentration (10-50 mg/l), catalyst dose (0.002-0.3 g), and PMS dose (0.02-0.1 g). Quenching experiments revealed that sulfate radicals are primarily responsible for rhodamine B degradation. A plausible mechanism for catalytic PMS activation was also proposed. Complete decolorization occurred within the first few minutes of the reaction. Furthermore, the catalytic activity of the CoFe₂O₄/Ag-fMWCNT/PMS hybrid nanocomposite remained stable after five successive cycles. This study verifies the applicability of CoFe₂O₄/Ag-fMWCNTs as an ultrafast catalyst for the complete removal of persistent organic pollutants via PMS activation, revealing their promising application in wastewater treatment.

Ag3PO4-based photocatalysts and their application in organic-polluted wastewater treatment

Semiconductor photocatalysis technology has shown great potential in the field of organic pollutant removal, as it can use clean and pollution-free solar energy as driving force. The discovery of silver phosphate (Ag₃PO₄) is a major breakthrough in the field of visible light responsive semiconductor photocatalysis due to its robust capacity to absorb visible light < 520 nm. Furthermore, the holes produced in Ag₃PO₄ under light excitation possess a strong oxidation ability. However, the strong oxidation activity of Ag₃PO₄ is only achieved in the presence of electron sacrifice agents. Otherwise, photocorrosion would greatly reduce the reuse efficiency of Ag₃PO₄. This review thus focuses on the structural characteristics and preparation methods of Ag₃PO₄. Particularly, the recent advances in noble metal deposition, ion doping, and semiconductor coupling, as well as methods of magnetic composite modification for the improvement of catalytic activity and recycling efficiency of Ag₃PO₄-based catalysts, were also discussed, and all of these measures could enhance the catalytic performance of Ag₃PO₄ toward organic pollutants degradation. Additionally, some potential modification methods for Ag₃PO₄ were also proposed. This review thus provides insights into the advantages and disadvantages of the application of Ag₃PO₄ in the field of photocatalysis, clarifies the photocorrosion essence of Ag₃PO₄, and reveals the means to improve photocatalytic activity and stability of Ag₃PO₄. Furthermore, it provides a theoretical and methodological basis for studying Ag₃PO₄-based photocatalyst and also compiles valuable information regarding the photocatalytic treatment of organic polluted wastewater.

A facile synthesis of Ag3PO4/BiPO4 p-n heterostructured composite as a highly efficient photocatalyst for fluoroquinolones degradation

Ag₃PO₄/BiPO₄ heterojunction photocatalysts with an intergrowth structure composed of sphere-shaped Ag₃PO₄ and nanorod BiPO₄ were synthesized via a facile combination of solvothermal method and in-situ deposition process. They exhibit enhanced photocatalytic activities under sunlight irradiation, and the heterojunction composite with the 10 wt% loading amounts of Ag₃PO₄ presented the highest photocatalytic activities against norfloxacin (NFX), ofloxacin (OFXL) and ciprofloxacin (CIP), with high degradation efficiencies of 94.7%, 95.4% and 92.1%, respectively. Additionally, the Ag₃PO₄/BiPO₄ photocatalyst demonstrates outstanding structural and photocatalytic stability. The superior performance was attributed to the effective charge transfer across the p-n heterojunction interface and the enhancement of light absorption. This work provides a new insight into the development of novel BiPO₄-based heterojunction composites and meets the remediation for contaminated aqueous environment.

Ag functionalized SnS2 with enhanced photothermal activity for safe and efficient wound disinfection

Severe bacterial infections have brought an urgent threat to our daily life, and photothermal therapy (PTT) has acted as an effective method to kill bacteria. Herein we decorated Ag on the surface of SnS₂ (Ag@SnS₂), which has outstanding photothermal conversion capability and good biocompatibility. The decoration of Ag on SnS₂ improved the absorption of near-infrared (NIR) light in comparison to SnS₂, resulting in a temperature increase of 50 °C after 5 min of NIR light irradiation (1.9 W cm^-2) and a photothermal conversion efficiency of 31.3%. Ag@SnS₂ exhibits almost 100% growth inhibition of E. coli and S. aureus bacteria due to hyperthermia, with a concentration larger than 0.5 mg mL^-1 and 5 min of NIR irradiation. Meanwhile, SEM images of treated bacterial cells showed the attachment of Ag@SnS₂ on the cell surface and obvious cellular membrane destruction. Ag@SnS₂ can also accelerate in vivo wound healing through PTT-induced bacterial disinfection. Therefore, Ag@SnS₂ exhibits great potential for photothermal antibacterial application and wound disinfection.

The application of FTO-Cu2O/Ag3PO4 heterojunction in the photoelectrochemical degradation of emerging pharmaceutical pollutant under visible light irradiation

We report the photoelectrochemical application of a visible light active FTO-Cu₂O/Ag₃PO₄ photoanode for the abatement of sulfamethoxazole in water. The as-synthesised photoanodes were characterised using XRD, field emission SEM, EDX, diffuse reflectance UV-vis, impedance spectroscopy and chronoamperometry. The results obtained confirmed a successful formation of p-n heterojunction at the Cu₂O/Ag₃PO₄ interface. The highest photocurrent response of 0.62 mAcm^-2 was obtained for the composite photoanode which was four times higher than pure Cu₂O and about three times higher than pristine Ag₃PO₄. The photoanode gave 67% removal efficiency within 2 h upon its photoelectrochemical application in the degradation of sulfamethoxazole with 1.5 V bias potential at pH 6.2. The FTO-Cu₂O/Ag₃PO₄ electrode was also applied in the treatment of a cocktail of synthetic organics containing sulfamethoxazole and orange II dye. The photogenerated holes was found to be the major oxidant and the photoanodes was stable and reusable.

In situ ultrasound-assisted ion exchange synthesis of sphere-like AgClxBr1-x composites with enhanced photocatalytic activity and stability

AgCl_xBr_1-x composites with different halogen molar ratios (Cl/Br) were prepared by a facile ultrasound-assisted ion-exchange method. The formation of close contact between AgCl and AgBr facilitated the transportation of photoexcited charge carriers and contributed to the enhanced visible-light-driven photocatalytic degradation of different kinds of antibiotics. The AgCl_xBr_1-x composites had a sphere-like morphology and tunable band gaps from 2.95 to 2.57 eV depending on Cl/Br mole ratios. Besides, the AgCl_xBr_1-x composite was optimized by varying halogen mole ratios (Cl/Br) to achieve the highest photocatalytic activity. Results indicated that AgCl_0.75Br_0.25 showed the best photocatalytic degradation performance, which was about 2.36 and 2.78 times that of the single AgCl towards ciprofloxacin (CIP) and metronidazole (MNZ) degradation, respectively. Meanwhile, a possible photocatalytic degradation mechanism was discussed, and results indicated that the holes (h⁺) and •OH were the dominant active species in the AgCl_0.75Br_0.25 system.

In-situ growth of high-density ultrafine Ag3PO4 nanoparticles on 3D TiO2 hierarchical spheres for enhanced photocatalytic degradation of organic pollutants

Silver phosphate (Ag₃PO₄, APO) has attracted intense attention as a visible-light-driven photocatalyst, but its large-scale application is limited by severe charge recombination and inevitable photo-corrosion. Various rational APO-based heterostructures composed of APO nanoparticles (NPs) and band-matched semiconductor support are designed to address the above issues. Nevertheless, the size, density, stability, and dispersion of APO NPs are critical challenges for the photocatalytic performance of APO-based photocatalysts. Here, three-dimensional (3D) self-assembled TiO₂ hierarchical spheres (THS) prepared by a simple one-step hydrothermal method are employed as innovative support, and ultrafine high-density APO NPs with an average size of about 3 nm are successfully deposited and uniformly dispersed throughout THS to form hierarchical THS/APO composites. The novel THS/APO microstructure provides abundant reactive sites for photocatalytic reactions and promotes the photogenerated charge separation and transfer due to the ultrafine size of APO NPs and the TiO₂/APO Type-II heterojunction. As a result, the THS/APO composites show significant improvement in photocatalytic activity and stability in methylene blue (MB) degradation. The reaction constant of THS/APO composites far exceeds that of either THS or APO, roughly 16 and 7 times higher than that of THS and APO under full-spectrum light, and 41 and 4 times higher under visible light. Our results strongly suggest new insights into the low-cost, large-scale application of high-efficiency APO-based photocatalyst.

BiOBr/Ag/AgBr heterojunctions decorated carbon fiber cloth with broad-spectral photoresponse as filter-membrane-shaped photocatalyst for the efficient purification of flowing wastewater

The development of recyclable photocatalysts with broad-spectral photoresponse has drawn much attention for the practical application in flowing wastewater treatment. Herein, we have reported the construction of BiOBr/Ag/AgBr junctions on carbon fiber cloth (CFC) as broad-spectral-response filter-membrane-shaped photocatalyst that is efficient and easily recyclable. With CFC as the substrate, BiOBr nanosheets (diameter: 0.5-1 μm) were firstly synthesized by a hydrothermal method, and then Ag/AgBr nanoparticles (size: 100-300 nm) were prepared on the surface of CFC/BiOBr by using a chemical bath deposition route. CFC/BiOBr/Ag/AgBr presents superior flexibility and wide UV-Vis-NIR photoabsorption (from 200 to 1000 nm). Under visible light irradiation, CFC/BiOBr/Ag/AgBr (area: 4 × 4 cm²) can remove 99.8% rhodamine B (RhB), 99.0% acid orange 7 (AO7), and 93.0% tetracycline (TC) after 120 min, better than CFC/BiOBr (95.4% RhB, 55.0% AO7 and 91.2% TC). Interestingly, when CFC/BiOBr/Ag/AgBr is served as a filter-membrane in a photoreactor to purify the flowing sewage (RhB, rate: ~1.5 L h^-1), the degradation rate of RhB goes up to 90.0% after ten filtering grades. Therefore, CFC/BiOBr/Ag/AgBr has great potential to purify the flowing wastewater as a novel filter-membrane-shaped photocatalyst.

Enhanced Photodegradation of Synthetic Dyes Mediated by Ag3PO4-Based Semiconductors under Visible Light Irradiation

Four silver phosphate-based materials were successfully synthesized, characterized, and evaluated, together with TiO2, in the photodegradation of synthetic dyes (tartrazine, Orange II, rhodamine, and Brilliant Blue FCF) under two irradiation sources centered at 420 and 450 nm. Scanning Electron Microscopy (SEM) images showed different topologies of the synthesized materials, whereas diffuse reflectance spectra demonstrated that they display absorption up to 500 nm. Degradation experiments were performed in parallel with the silver materials and TiO2. Upon irradiation centered at 420 nm, the abatement of the dyes was slightly more efficient in the case of TiO2—except for Orange II. Nevertheless, upon irradiation centered at 450 nm, TiO2 demonstrated complete inefficiency and silver phosphates accomplished the complete abatement of the dyes—except for Brilliant Blue FCF. A careful analysis of the achieved degradation of dyes revealed that the main reaction mechanism involves electron transfer to the photogenerated holes in the valence band of silver photocatalysts, together with the direct excitation of dyes and the subsequent formation of reactive species. The performance of TiO2 was only comparable at the shorter wavelength when hydroxyl radicals could be formed; however, it could not compete under irradiation at 450 nm since the formed superoxide anion is not as reactive as hydroxyl radicals.

An efficient and robust exfoliated bentonite/Ag3PO4/AgBr plasmonic photocatalyst for degradation of parabens

Efficient visible-light-driven heterojunction photocatalysts have attracted broad interest owing to their promising adsorption and degradation performances in the removal of organic pollutants. In this study, a mesoporous exfoliated bentonite (EB)/Ag₃PO₄/AgBr (30%) photocatalyst was obtained by stripping and exfoliating bentonite as the support for loading Ag₃PO₄ and AgBr. The particle size ranges of Ag₃PO₄ and AgBr were about 10–30 nm and 5–10 nm, respectively. The exfoliated bentonite could greatly improve the dispersion and adsorption of Ag₃PO₄ and AgBr, and significantly enhance the stability of the material during paraben photodegradation. 0.2 g L⁻¹ methylparaben (MPB) was completely decomposed over the EB/Ag₃PO₄/AgBr (30%) in 40 min under visible light irradiation. In addition, the photocatalytic activity of EB/Ag₃PO₄/AgBr (30%) remained at about 91% after five recycling runs manifesting that EB/Ag₃PO₄/AgBr (30%) possessed excellent stability. Radical quenching tests revealed that holes (h⁺) and hydroxyl radicals (·OH) were the major radicals. They attacked the side chain on the benzene ring of parabens, which were gradually oxidized to the intermediates, such as benzoic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, azelaic acid, and eventually became CO₂ and H₂O. The enhancement of photocatalytic activity and photo-stability could be ascribed to the stable structural characteristics, enlarged surface area, high absorption ability, and improved light absorption ability from loading Ag₃PO₄ onto EB. Meanwhile, the matched energy levels of Ag₃PO₄ and AgBr made the photoelectron–hole pairs separate and transfer effectively at the interfaces. As a result, the photocatalytic properties of EB/Ag₃PO₄/AgBr (30%) composites were enhanced.

A mesoporous exfoliated bentonite (EB)/Ag₃PO₄/AgBr (30%) photocatalyst was designed to combine various functions to achieve efficient photodegradation of parabens.

Graphene modified anatase/titanate nanosheets with enhanced photocatalytic activity for efficient degradation of sulfamethazine under simulated solar light

Graphene modified anatase/titanate nanosheets (G/A/TNS) synthesized through hydrothermal treatment were used for solar-light-driven photocatalytic degradation of a typical pharmaceutically active compound, sulfamethazine (SMT). The optimal material was synthesized with 0.5 wt% of graphene loading (G/A/TNS-0.5), which could efficiently degrade 96.1% of SMT at 4 h. G/A/TNS-0.5 showed enhanced photocatalytic activity compared with the neat anatase and unmodified anatase/titanate nanosheets (A/TNS). UV-vis diffuse reflection spectra indicated that G/A/TNS-0.5 had a lower energy band gap (E_g) of 2.8 eV than A/TNS (3.1 eV). The grafted graphene acted as an electron transfer mediator after photoexcitation, resulting in inhibition on rapid recombination of electron-hole pairs. More importantly, architecture of graphene and titanate nanosheets both with two-dimensional structures greatly facilitated the photoexcited electron transfer. •OH and ¹O₂ were the primary reactive oxygen species (ROS) to SMT degradation. Fukui index (f^-) derived from density functional theory (DFT) calculation predicted the active sites on SMT molecule, and then SMT degradation pathway was proposed by means of intermediates identification and theoretical calculation. Furthermore, G/A/TNS-0.5 could be well reused and 90.5% of SMT was also degraded after five runs. The developed new photocatalysts show great potential for degradation of emerging organic contaminants through photocatalysis under solar light.

Photocatalytic degradation of trihalomethanes and haloacetonitriles on graphitic carbon nitride under visible light irradiation

Trihalomethanes (THMs) and haloacetonitriles (HANs), most common disinfection by-products in drinking water, pose adverse environmental impacts and potential risks to human health. There is a pressing need to develop innovative, economically feasible, and environmentally benign processes to control these persistent contaminants. In this paper, visible-light-responsive graphitic carbon nitride (g-C₃N₄) samples were synthesized to degrade the THMs and HANs and the photocatalytic degradation mechanism was explored. The results indicated that a carbon-doped g-C₃N₄ with an optimum dopant content (MCB_0.07) displayed the best photocatalytic activity for the total trihalomethanes (TTHM) and total haloacetonitriles (THAN), with the reaction rate constant of 11.6 and 10.4 (10^-3 min^-1), respectively. MCB_0.07 demonstrated a high THMs and HANs removal efficiency under visible light irradiation and could be reused. According to scavenger tests of the selected reactive species and X-ray photoelectron spectroscopy, holes play a dominant role for both THMs and HANs degradation on the MCB_0.07. The degradation of HANs by holes proceeded mainly through breakage of the CC bond in the CCN group. The THMs degradation was achieved through hydrogen abstraction or/and dehalogenation. The brominated-THMs/HANs were more photosensitive than their chlorinated analogous and were less stable than bromo-chloro-THMs/HANs. This study sheds light on the mechanism of the photocatalytic degradation of THMs and HANs under visible light irradiation by carbon-doped g-C₃N₄. Furthermore, it could provide insights for engineering applications and contaminant control in drinking water purification.

Continuous Flow Removal of Anionic Dyes in Water by Chitosan-Functionalized Iron Oxide Nanoparticles Incorporated in a Dextran Gel Column

This paper describes a novel chromatographic method for efficient removal of anionic dyes from aqueous solutions. Chitosan-coated Fe₃O₄ nanoparticles can easily be immobilized on a dextran gel column. Single elution of Evans Blue (EB) solution to the nanoadsorbent-incorporated columns provides high removal efficiency with a maximum adsorption capacity of 243.9 mg/g. We also investigated the influence of initial concentration and solution pH on the removal efficiency of EB. The electrostatic interaction between the adsorbent surface and negatively charged sulfate groups on EB molecules promotes the efficient adsorption of dyes. The equilibrium data matched well with the Langmuir isotherm model, which indicated monolayer dye adsorption onto the adsorbent surface. To extend the application of the current method, we performed further adsorption experiments using other anionic dyes of different colors (Cy5.5, Acid Yellow 25, Acid Green 25, and Acid Red 1). All of these molecules can efficiently be captured under continuous flow conditions, with higher removal efficiency obtained with more negatively charged dyes. These findings clearly demonstrate that the present approach is a useful method for the removal of anionic dye contaminants in aqueous media by adsorption.

Degradation of antibiotics in multi-component systems with novel ternary AgBr/Ag3PO4@natural hematite heterojunction photocatalyst under simulated solar light

Abatement of antibiotics from aquatic systems is of great importance but remains a challenge. Herein, we prepared ternary AgBr/Ag₃PO₄@natural hematite (AgBr/Ag₃PO₄@NH) heterojunction composite via a simple route for the photocatalytic degradation of antibiotic pollutants. By adjusting the dose of Ag species, four products with different Ag content (denoted as Ag_0.5BrPFe, Ag₁BrPFe, Ag_1.5BrPFe, and Ag₂BrPFe) were developed. Among them, Ag_1.5BrPFe exhibited the best photocatalytic activity. Four antibiotics (i.e. ciprofloxacin (CIP), norfloxacin (NOR), sulfadiazine (SDZ), and tetracycline (TTC)) could be degraded with synthesized Ag_1.5BrPFe in multi-component systems. Water matrix indexes including solution pH, coexisting anions, humic acids exhibited distinct effects on the degradation process. The results revealed that the degradation process was accelerated at acidic conditions while depressed at basic conditions. Superoxide radical and hole were detected by in situ electron spin resonance technique and played the dominant roles. The degradation pathway TTC was tentatively established followed with the identification of the degradation intermediates and computational analysis. This work would shed light on the photocatalytic degradation mechanism of organic pollutants by the AgBr/Ag₃PO₄@NH composite.

AgBr/(Sr0.6Bi0.305)2Bi2O7 Heterostructured Composites: Fabrication, Characterization, and Significantly Enhanced Photocatalytic Activity

The pyrochlore-type (Sr0.6Bi0.305)2Bi2O7 (SBO) containing Bi3+ and Bi5+ mixed valent states was first investigated as a photocatalyst in our very recent work. To further improve the photocatalytic performance, AgBr/SBO heterostructured composites were synthesized by using a deposition-precipitation method. The characterization of phase structure, morphology, microstructure, elemental composition, and optical properties of the obtained products were performed using X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM)TEM, X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy (UV-vis DRS). The photocatalytic activity of samples was evaluated by degrading methylene blue under visible light illumination. AgBr/SBO composites possess high stability and significantly enhanced photocatalytic performance. The improvement of photocatalytic activity is due to the enhanced light absorption and the separation of photoinduced electrons and holes on the interface of AgBr/SBO heterostructured composites.

Photocatalytic removal of phenanthrene and algae by a novel Ca-Ag3PO4 composite under visible light: Reactivity and coexisting effect

In this study, the feasibility of a novel Ca-Ag₃PO₄ composite with visible light irradiation for the phenanthrene (PHE) degradation and algae inactivation in artificial seawater was firstly investigated. The experimental findings revealed that Ag₃PO₄ phase was sucessfully formed on the Ca-based material, and the presence of Ca-based material could effectively keep Ag₃PO₄ particles stable. An excellent performance on PHE degradation or algae inactivation was observed from Ca-Ag₃PO₄ composite under visible light irradiation. The degradation of PHE or inactivation of algae not only could be efficiently achieved in the single mode, but also could be successfully achieved in the coexisting mode. Above 96% of PHE and algae were simultaneously removed within 12 h in the Ca-Ag₃PO₄/visible light system. It was further observed that the degradation of PHE and/or inactivation of algae increased with the increase of Ca-Ag₃PO₄ dosage. HO was the primary radical responsible for PHE degradation, whereas HO and Ag⁺ released from Ca-Ag₃PO₄ mainly contributed to the algae inactivation. A possible mechanism involving the catalytic removal of PHE and algae by Ca-Ag₃PO₄ under visible light irradiation was proposed. This study provides helpful guide for the simultaneous removal of various pollutants in real seawater.

Superior disinfection effect of Escherichia coli by hydrothermal synthesized TiO2-based composite photocatalyst under LED irradiation: Influence of environmental factors and disinfection mechanism

The photocatalytic inactivation of Escherichia coli (E. coli) under light-emitting diode (LED) light irradiation was performed with P/Ag/Ag₂O/Ag₃PO₄/TiO₂ photocatalyst to investigate the photocatalytic bactericidal activity. Our work showed that this composite photocatalyst possessed remarkable bacterial disinfection ability and could completely inactivate 10⁸ cfu/mL of E. coli within just 40 min under the optimum catalyst loading of 0.5 g/L. The effects of different environmental factors, including light wavelength, light intensity, temperature, solution pH and inorganic ions, on the inactivation efficiency were evaluated. The results showed that bacteria inactivation by P/Ag/Ag₂O/Ag₃PO₄/TiO₂ was more favorable with blue colored LED irradiation, light intensity at 750 W/m², temperature in the range of 30-37 °C and pH values at natural or slightly alkaline condition. The existence of different inorganic ions under normal environmental level had no significant impact on the bactericidal performance. In addition, during the inactivation process, the morphology changes of E. coli cells were directly observed by scanning electron microscope (SEM) and further proved by the measurement of K⁺ leakage from the inactivated E. coli. The results demonstrated that the photocatalytic inactivation caused drastic damage on bacterial cells membrane. Furthermore, the mechanisms of photocatalytic bacterial inactivation were also systemically studied and the results confirmed that the excellent disinfection activity of P/Ag/Ag₂O/Ag₃PO₄/TiO₂ resulted from the major reactive species: h⁺ and ·O₂^- from photocatalytic process instead of the leakage of Ag⁺ (≤0.085 ± 0.005 mg/L) from photocatalyst. These results indicate that P/Ag/Ag₂O/Ag₃PO₄/TiO₂ photocatalyst has promising potential for real water sterilization application.

Preparation and visible-light photocatalytic properties of the floating hollow glass microspheres – TiO2/Ag3PO4 composites

The amino modified low-density hollow glass microspheres were used as carriers of TiO₂ and Ag₃PO₄ photocatalysts to prepare the floating visible-light photocatalyst composite.

Nanostructured g-C3N4/AgI composites assembled by AgI nanoparticles-decorated g-C3N4 nanosheets for effective and mild photooxidation reaction

AgI nanoparticles-decorated g-C₃N₄ nanosheets with enhanced visible-light photocatalytic activity for the mild photooxidation of 1,4-DHP into its pyridine derivatives.

Synthesis of magnetic functionalized MWCNT nanocomposite through surface RAFT co-polymerization of acrylic acid and N-isopropyl acrylamide for removal of cationic dyes from aqueous solutions

In this study, magnetic multi-walled carbon nanotube (MMWCNT) composites were prepared via surface reversible addition fragmentation chain transfer (RAFT) co-polymerization of acrylic acid (AA) and N-isopropyl acrylamide (NIPAM) in the presence of Fe₃O₄ nanoparticles. First, a novel RAFT agent (RA) was prepared and then immobilized onto the surface of MWCNT to fabricate RA-g-MWCNT. Then, Fe₃O₄ nanoparticles were attached onto the surface of RA-g-MWCNT. Finally, RAFT co-polymerization of AA and NIPAM monomers was carried out via Fe₃O₄-g-RA-g-MWCNT RAFT agent. The structure and morphology of the prepared polymer-coated MWCNT was examined by FTIR, SEM, TEM, XRD, VSM, and TGA. The adsorption behaviours of the cationic dyes were studied. The equilibrium isotherm and kinetics of cationic dyes were investigated. Thermodynamics investigations also depicted that the adsorptions of cationic dyes were spontaneous and endothermic in nature. The synthesized dye adsorbent with high adsorption capacities, reusability, and easy recovery makes it as a good candidate for wastewater treatment.