Anti-photocorrosion Performance Research Articles

Selective Oxygen Activation to Reactive Oxygen Species on a Carbon Layer-Encapsulated CuxO Electrocatalyst for Water Purification.

In situ synthesis of reactive oxygen species (ROS) on demand via oxygen activation (OA) is significant in biological, chemical, and environmental fields. Thus, the design of OA catalysts with adequate reactivity, durability, and selectivity is critical but challenging. Here, we report a CuxO@C core@shell photoelectrode prepared by encapsulating Cu/Cu2O/CuO into a carbon layer through anodic electropolymerization (electrophoresis-coupled self-assembly of carbon quantum dots). Theoretical prediction and experiments indicate that the carbon layer can effectively facilitate optical trapping and charge transfer, thus promoting photoelectric conversion and anti-photocorrosion performance of CuxO@C. The inner CuxO core acts as an electron reservoir and continuously injects electrons into the outer carbon layer shell, and the carbon atoms adjacent to oxygen-enriched functional groups (C-O-C and -COOH) in the electron-rich carbon layer work as the reactive sites to adsorb O2 and donate electrons to the antibonding orbital [lowest unoccupied molecular orbital (π*)] of dioxygen. Optimized adsorption and hydrogenation of the critical intermediates (*O2, *OOH, and *H2O2) and thermodynamically tunable O-O bond cleavage enable O2 being selectively reduced to the superoxide anion and hydroxyl radical via the mixed multielectron processes consisting of one- and three-electron pathways. Sulfamethoxazole, an emerging refractory organic contaminant widely present in the environment, can be effectively degraded (∼100% removal) in such an electrochemical platform, benefiting from the abundant ROS generated in situ. Our findings demonstrate an innovative strategy to develop highly efficient and selective OA catalysts for practical water purification.

Formation of Ag3PO4/AgBr composites with Z-scheme configuration by an in situ strategy and their superior photocatalytic activity with excellent anti-photocorrosion performance

A novel Ag3PO4/AgBr composite with Z-Scheme structure was constructed and synthesized via a simple in situ ion-exchange strategy on the surface of Ag3PO4 tetrahedra in an alkaline environment. The as-prepared Ag3PO4/AgBr composite has an intimate contact interface and exhibited enhanced visible-light photocatalytic activity, accompanied by superior stability toward degradation of methylene blue (MB) in aqueous solution. Also, a variety of pollutants can be degraded without selectivity, and the degradation efficiency was over 96%. Changes in the bandgap and the detailed degradation mechanism of the Ag3PO4/AgBr composite were analyzed and revealed using characterization analysis, theoretical calculations, and further designed experiments. Sufficient interfacial contact between Ag3PO4 and AgBr was favorable for transferring carriers and lengthening the lifetime of the Z-Scheme system, which simultaneously inhibit photocorrosion and maintain a high degradation rate. The trapping experiments indicate that h+ is a dominant reactive species for the degradation of MB. This Ag3PO4/AgBr photocatalyst with Z-Scheme structure shows great potential for replication and large scale impact on the environmental purification of organic pollutants.

Visible photoactivity and antiphotocorrosion performance of CdS photocatalysts by the hybridization of N-substituted carboxyl group polyaniline

In the paper, we report on the visible photocatalytic activity and antiphotocorrosion performance of CdS quantum dots (CdSQDs) by the combination of polyaniline with the modification of the carboxyl group, which was prepared by an N-substituted carboxyl group polyaniline (NPAN) cadmium precursor. The photocurrent response and photodegradation of Rhodamine B experiments show a higher current output and photocatalytic activity for the CdSQDs/NPAN hybrid photocatalysts in comparison with the mechanical blends of CdS nanoparticles and NPAN, as well as pure CdS nanoparticles. The enhanced photocatalytic performance could be attributed to the hybrid effect between CdSQDs and the carboxyl group in the polyaniline matrix. TEM morphology and XRD patterns of CdSQDs/NPAN hybrids had no significant differences before and after the photocatalytic oxidation, indicating that the incorporation of the carboxyl group in polyaniline could completely inhibit the photocorrosion of the CdS semiconductor. A possible photocatalytic mechanism of the CdSQDs/NPAN hybrid photocatalysts was proposed in accordance with the experimental results.

Ag3PO4/Ti3C2 MXene interface materials as a Schottky catalyst with enhanced photocatalytic activities and anti-photocorrosion performance

The high carrier recombination rate and serious photocorrosion of Ag3PO4 greatly restrict its photocatalytic application. Here, we fabricated an Ag3PO4/Ti3C2 Schottky catalyst and found that Ti3C2 can greatly enhanced the catalytic activity and stability of Ag3PO4. This arises from: (i) the abundant surface hydrophilic functional groups of Ti3C2 construct strong interfacial contact with Ag3PO4, which facilitate the separation of carriers; (ii) the strong redox reactivity of surface Ti sites promote multiple electron reduction reactions to induce more OH production; and (iii) a Schottky junction formed at Ag3PO4-Ti3C2 interface timely transfer electrons to Ti3C2 surface by built-in electric field, inhibiting the photocossion of Ag3PO4 caused by photogeneration electrons. Consequently, Ag3PO4/Ti3C2 exhibited excellent photocatalytic activity and stability for the degradation of organic pollutants. Especially, the apparent rate constant of 2,4-Dinitrophenol degradation with Ag3PO4/Ti3C2 was 2.5 times that of Ag3PO4/RGO and 10 times that of Ag3PO4. The photocatalytic performance of Ag3PO4/Ti3C2 toward tetracycline hydrochloride still maintained 68.4% after 8 cycles, while Ag3PO4/RGO and Ag3PO4 only maintained 36.2% and 7.8%, respectively. Furthermore, the efficient photoreduction of Cr6+ using AgI/Ti3C2 further illustrated an enormous potential in coupling Ti3C2 with other photosensitivity semiconductor to improve their catalytic activity and stability.

Core-shell Ag2CrO4/N-GQDs@g-C3N4 composites with anti-photocorrosion performance for enhanced full-spectrum-light photocatalytic activities

It is a challenge to develop highly efficient and stable photocatalysts to harvest solar spectrum as broad as possible. In this work, for the first time, a nitrogen-doped graphene quantum dots (N-GQDs) modified Ag2CrO4@g-C3N4 core-shell structured composite was fabricated to achieve full-spectrum response from UV to near-infrared (NIR) region. In the Ag2CrO4/N-GQDs@g-C3N4 composites, Ag2CrO4 and g-C3N4 can be excited by UV and visible light, and N-GQDs can absorb NIR light to emit visible light, which greatly enhances the utilization of solar light. Moreover, compared with the normal hybrid heterojunctions, the core-shell structure provides larger contact area between Ag2CrO4 and g-C3N4. The large contact area and highly conductive N-GQDs effectively promote the photoelectron transfer from Ag2CrO4 to g-C3N4, which not only restrains the charge combination, but also greatly inhibits the photocorrosion of Ag2CrO4. The cycle experimental results showed that the performance of AN@CN did not decrease even after eight cycles of usage, and the XRD and EIS results also confirmed the stable nature of AN@CN composites. As a result, the optimized composites exhibit excellent photocatalytic degradation of doxycycline under full-spectrum light, and the possible photocatalytic mechanism was proposed. This work provides guidance for the design of high efficient photocatalysts with full-spectrum response and excellent stability.

Novel 3D core-shell structured CQDs/Ag3PO4@Benzoxazine tetrapods for enhancement of visible-light photocatalytic activity and anti-photocorrosion

To improve the visible-light photocatalytic activity and anti-photocorrosion of Ag3PO4, novel 3D core-shell CQDs/Ag3PO4 @benzoxazine tetrapods with more exposure of {110} facets of Ag3PO4 has been successfully synthesized for the first time by electrochemical oxidation, chemical precipitation and molecular self-assembly reaction. In CQDs/Ag3PO4@benzoxazine tetrapods, CQDs could not only induce more photocarrier generation from high-energy facets of Ag3PO4 tetrapods but also accelerate the electrons transfer from conduction band of Ag3PO4 tetrapods to the bottom of conduction band of CQDs. Furthermore, silver amine complex could act as a bridge for the photo-electrons flowing from core to shell, which is beneficial to the subsequent free radical chain reaction. In addition, the 3D core-shell structure decreased the solubility of Ag3PO4. UV–vis DRS, indicating that the band gap of CQDs(0.38%)/Ag3PO4 @benzoxazine (1.65 eV) was far less than that of Ag3PO4 tetrapods (2.0 eV) and traditional Ag3PO4 (2.45 eV). Moreover, the photocurrent tests showed that CQDs(0.38%)/Ag3PO4@benzoxazine had perfect drift ability of generated photocarriers. Accordingly, the CQDs(0.38%)/Ag3PO4@benzoxazine tetrapods exhibited excellent visible-light photocatalytic activity and anti-photocorrosion performance. More than 93% of Methylorange and rhodamine B could be photodegraded within 16 min and 10 min over CQDs(0.38%)/Ag3PO4@benzoxazine tetrapods, respectively. Even after 9 cycles, CQDs(0.38%)/Ag3PO4@benzoxazine could still remain 95% removal rate of sulfamethoxazole (SMX) with 10 min. Through recycling catalytic experiments and photodegradation pathway explore of SMX, the CQDs(0.38%)/Ag3PO4@benzoxazine composite suggest its great mineralization capability on sulfonamide antibiotics. The free radicals trapping experiments demonstrated that the holes photoinduced were the main active oxidizing species which played the dominant role in the photocatalytic process. Thus, CQDs(0.38%)/Ag3PO4@benzoxazine is a promising visible-light responses catalyst for photodegradation of organic pollutants in the environmental protection.

One-pot, facile fabrication of a Ag3PO4-based ternary Z-scheme photocatalyst with excellent visible-light photoactivity and anti-photocorrosion performance

Ag3PO4 can-not be widely used as an efficient photocatalyst in practical applications because of its susceptibility to photocorrosion. In this study, a novel, ternary Z-scheme photocatalytic system containing graphene oxide (GO), Ag3PO4 and SnS2 was fabricated by a one-pot, mild, in-situ precipitation method successfully. Using Rhodamine B (RhB) as the target of elimination, GO/Ag3PO4/SnS2 exhibited outstanding photocatalytic and anti-photocorrosion properties compared with those of Ag3PO4, Ag3PO4/SnS2 and GO/Ag3PO4. RhB was thoroughly degraded over the optimized GO/Ag3PO4/SnS2 nanocomposite after only 15 min under visible-light irradiation; this result is approximately 2.14, 3.33 and 5.83 times faster than that of GO/Ag3PO4, Ag3PO4/SnS2 and Ag3PO4, respectively. After three reuses, the photocatalytic activity of the ternary composite slightly decreased but remained 2.36, 4.08 and 12.70 times higher than those of the reused GO/Ag3PO4, Ag3PO4/SnS2 and Ag3PO4, respectively. In this system, the efficient separation and migration of the photoinduced current carriers in Ag3PO4 was realized through a double Z-scheme electron-transfer mechanism in which the GO nanosheets acted as the photocatalyst and electron mediator, thereby enhancing the photoactivity and stability of Ag3PO4. The present study provides a new perspective for enhancing photocatalytic and anti-photocorrosion performances in perishable photocatalysts for organic sewage and other environmental contamination treatments.

An environmentally friendly Z-scheme WO3/CDots/CdS heterostructure with remarkable photocatalytic activity and anti-photocorrosion performance

As a representative artificial photosynthetic system, direct Z-scheme WO3/CdS is a promising photocatalyst system for water purification. However, this system is still limited due to low electron transfer efficiency and serious photocorrosion. Here, we designed and precisely fabricated a novel all-solid-state Z-scheme WO3/CDots/CdS system. The CDots, as a nonmetallic electron mediator, could promote interfacial charge carrier separation and eliminate photocorrosion with enhanced photocatalytic activity. The phase, morphologies, microstructures, and optical and electrical properties of as-obtained Z-scheme WO3/CDots/CdS heterojunctions were investigated in detail. The photocatalytic performance of as-prepared catalysts was evaluated by the decomposition of 4-chlorophenol (4-CP), rhodamine B (RhB), and tetracycline hydrochloride (TCH) and the reduction of aqueous Cr(VI) in visible light. The optimized Z-scheme WO3/CDots/CdS-2 photocatalyst exhibited the highest photocatalytic activity for degrading and mineralizing 4-CP (∼70.0% and 48.3% in 7 h, respectively), both of which exceeded the rates observed in WO3/CdS samples under the same conditions by ∼2 times. In addition, the WO3/CDots/CdS-2 showed excellent stability and reusability with negligible change at ∼2.2% difference for 4-CP degradation in eight cycles. The release percentage of SO42− (transformed from S2−) and Cd2+ was only ∼0.77% and 0.79%, respectively, when compared with the initial concentration, which was far less than for the WO3/CdS system (∼5.64% and 5.70%). The results indicated that a thorough and complete Z-scheme charge carrier transfer route was achieved. Toxicity assessment authenticated good biocompatibility and low cytotoxicity of WO3/CDots/CdS. This study showed that the Z-scheme WO3/CDots/CdS was a promising photocatalyst for water purification.

Silver phosphate-based Z-Scheme photocatalytic system with superior sunlight photocatalytic activities and anti-photocorrosion performance

The serious photocorrosion of silver phosphate (Ag3PO4) has limited its practical applications. In this work, we propose a strategy to suppress its photocorrosion by the construction of a Z-Scheme photocatalytic system, which composed of reduced graphene oxide-enwrapped Ag3PO4 (Ag3PO4@RGO) and La,Cr-codoped SrTiO3 (La,Cr:SrTiO3). Dramatically, this system shows superior anti-photocorrosion and photocatalytic performances in degradation of both RhB and 2,4-DNP. Especially for RhB, it can be completely degraded after only 5min under intense sunlight irradiation. The improved photoactivity and anti-photocorrosion of Ag3PO4@RGO@La,Cr:SrTiO3 can be attributed to the following: (i) The sufficient interfacial contact between Ag3PO4 and RGO is favorable to transfer the carriers and lengthen the lifetime of it; (ii) the package of Ag3PO4 with RGO could work as a sheltering layer to protect Ag3PO4 from photocorrosion. (iii) The aggregation of photogenerated holes in the VB of Ag3PO4 makes it a rich-hole region due to Z-Scheme electrons transport mechanism, which can protect Ag3PO4 from the photo-reduction. This strategy provides a new thought of protecting photosensitive semiconductor from photocorrosion and could regard as an efficient application method for environmental cleaning under natural sunlight irradiation. Furthermore, it even could be extended to outdoor or indoor air cleaning in the future.

Preparation of three-dimensional Ag3PO4/TiO2@MoS2 for enhanced visible-light photocatalytic activity and anti-photocorrosion

We synthesized novel three-dimensional photocatalyst (Ag3PO4/TiO2@MoS2) with various content of TiO2@MoS2 by electrospining, sequential hydrothermal reaction and chemical deposition. The optimal content of TiO2@MoS2 in Ag3PO4/TiO2@MoS2 composites is 3.5wt%, and the bandgap of Ag3PO4/TiO2@MoS2 (3.5wt%) (1.85eV) was much lower than that of pure Ag3PO4 (2.45eV). Due to high conductivity of TiO2@MoS2 heterostructure, the separation efficiency of electron-hole pairs of Ag3PO4 was significantly improved so that Ag3PO4/TiO2@MoS2 (3.5wt%) presented higher photocatalytic activity. More than 92% Methyl orange and Methylene blue were photodegraded over Ag3PO4/TiO2@MoS2 (3.5wt%) in 12min and 5min, respectively. More importantly,TiO2@MoS2 could play the role of ‘wire’ to guide electrons captured by MoS2 and quickly transferred electrons into solution so that the recombination of electron-hole pairs and the reduction of silver irons were effectively restrained. Thus, Ag3PO4/TiO2@MoS2 (3.5wt%) exhibited excellent anti-photocorrosion performance. Even after 10 cycling runs, Ag3PO4/TiO2@MoS2 (3.5wt%) could degrade 75% and 92% of oxytetracycline and enrofloxacin, respectively, whereas Ag3PO4 degraded 23% and 44%. In addition, the possible photodegradation pathways of oxytetracycline and enrofloxacin were proposed, demonstrating that the photodegradation mechanisms involving oxidizing/shedding of functional groups firstly and opening the ring sequentially. Further detection of reactive oxidative species indicated that holes were the main active oxidizing species involved in the photocatalytic reaction process. Thus, Ag3PO4/TiO2@MoS2(3.5wt%) is a promising photocatalyst for photodegradation of organic pollutants in the environmental protection.

Improved visible-light photocatalytic activity and anti-photocorrosion of CdS nanoparticles surface-modified by conjugated derivatives from polyvinyl chloride

Cadmium sulfide (CdS) nanoparticles were surface-modified by conjugated polymer (CPVC) derived from conventional polyvinyl chloride (PVC) via heat-treatment at 150°C. The as-prepared CPVC/CdS nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (UV–vis DRS), photoluminescence spectroscopy (PL), electrochemical impedance spectroscopy (EIS), and photocurrent (Iph). The visible-light photocatalytic activity and stability of the nanocomposites were investigated by evaluating photodegradation of methyl orange (MO) and phenol, and their anti-photocorrosion performance was investigated by determining the concentrations of Cd2+ in the photodegrading systems under visible light irradiation. The results show that a small amount of CPVC on the surface of CdS nanoparticles hardly changes their crystallinity and sizes, while significantly improves their absorption in visible light range and separation efficiency of photogenerated electrons and holes. The CPVC/CdS nanocomposites exhibit much higher visible-light photocatalytic activity and anti-photocorrosion performance than pure CdS, and show good visible-light photocatalytic stability. The visible-light photocatalytic mechanism has been discussed.

Enhanced Photocurrent Responses and Antiphotocorrosion Performance of CdS Hybrid Derived from Triple Heterojunction

The enhanced photocurrent responses and dramatic antiphotocorrosion performance of CdS hybrid were obtained by formation of triple heterojunction (TH), i.e., n-CdS/n-TiO2/p-BDD:n-TiO2 cube tubes were vertically grown on p-type boron-doped diamond (BDD) film. Then n-CdS nanoparticles (NPs) were randomly assembled onto the surface of TiO2 and BDD, forming a film of CdS NPs. This triple heterojunction CdS hybrid reveals 36.5% improvement of initial photocurrent and 78% reduction of photocorrosion rate in contrast with that of the coupled CdS/TiO2 hybrid, which has only single heterojunctions (SH). The mechanisms of TH on charge separation and transport during the photocatalytic reaction have been emphasized. Except for the CdS/TiO2 (n–n) heterojunction, another two p–n heterojunctions, i.e., p-BDD/n-CdS and p-BDD/n-TiO2 exist in the TH. The conduction band (CB) position of TiO2 is lower than the corresponding band positions of CdS and BDD, so TiO2 can act as an acceptor for the photogenerated electrons. Also...

Visible photoactivity and antiphotocorrosion performance of PdS–CdS photocatalysts modified by polyaniline

PdS–CdS modified by polyaniline (PANI) as a novel photocatalyst was synthesized via a sonochemical approach for the first time. The as-prepared photocatalysts were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–vis absorption spectra, FT-IR spectra, and fluorescence spectra (PL). Under visible light, the photocatalysts showed excellent photocatalytic activity for hydrogen evolution in the absence of noble metal Pt and the antiphotocorrosion performance of the composite photocatalyst was also found to be significantly improved simultaneously compared to PdS–CdS without PANI modification. The highest rate for H 2 evolution was 3.32 mmol/h with the concentration of 1 wt.%PANI and 1 wt.%PdS.

Significant Visible Photoactivity and Antiphotocorrosion Performance of CdS Photocatalysts after Monolayer Polyaniline Hybridization

The dramatic enhanced visible light photocatalytic activity and excellent antiphotocorrosion performance of CdS photocatalysts were obtained after hybridized by monolayer polyaniline. The as-prepared PANI-CdS hybrid photocatalysts reveal the outstanding photocatalytic activity and photoelectrical conversion efficiency which can improve about 2.5 and 1.8 times that of the pure CdS, respectively. Significantly, the issue of photocorrosion, a congenital disadvantage of CdS photocatalysts, has been solved completely after hybridization. The mechanisms on enhancement of photocatalytic activity and antiphotocorrosion performance have been emphasized. Under visible light irradiation, photogenerated electrons in LUMO of PANI injected into the conduction band of CdS, photogenerated holes in the valence band of CdS transferred to the photocatalysts surface through HOMO of PANI. The rapid transferring of hole and high separation efficiency of electron−hole pairs lead to the dramatically enhanced photoactivity and completely inhibited photocorrosion.