Photoinduced Holes Research Articles

Rational design and construction of S-scheme CeO2/AgCl heterojunction with enhanced photocatalytic performance for tetracycline degradation

Semiconductor-based photocatalysis has attracted extensive attentions in waste water treatment and environment remediation. However, a single semiconductor photocatalyst inevitably encounters a dilemma between light absorption and redox ability of photoinduced holes and electrons. In this work, an S-scheme CeO2/AgCl heterojunction photocatalyst was designed, prepared and characterized by various techniques. The as-prepared CeO2/AgCl composite photocatalyst exhibited enhanced photocatalytic activity compared with single CeO2 and AgCl as revealed by the photodegradation of tetracycline (TC), a widely used antibiotic. According to UV–Vis spectral changes and degradation mass spectra of TC, the CeO2/AgCl composite photocatalyst not only can destroy the B, C, D rings, but also the A ring of TC, which cannot be destroyed by most of previously reported photocatalysts. The enhanced photocatalytic ability of CeO2/AgCl composite was due to the formation of an S-scheme heterojunction structure between CeO2 and AgCl, which simultaneously retained the maximum redox ability of photoinduced holes and electrons in the valence band of AgCl and in the conduction band of CeO2, respectively, resulting in the production of highly efficient O2−, OH and h+. This work provided insight into the rational design and construction of S-scheme heterojunction composites and new possibility of photocatalytic degradation of antibiotic wastewater.

Synergizing interstitial K and substitutional O by dual-doping on carbon nitride for efficient CO2 photoreduction

Photocatalytic CO2 reduction is a promising tactic to fix surplus CO2 and generate high-value products. Non-metallic graphitic carbon nitride (CN) is a robust and inexpensive photocatalyst for CO2 reduction, yet its efficiency remains limited by poor light absorption, sluggish charge kinetics, and low surface area. Here, we report K and O dual-doped CN (K/O-CN) synthesized by facile molten salt calcination for efficient CO2 photoreduction. Distinctive from CN, K/O-CN owned regular nanorod structure and introduced cyano terminal groups, due to the reconstruction of C-N bond by interstitial K doping and substitutional doping of O within CN matrix. K/O-CN displayed a CO production rate of 4.5 ± 0.2 μmol g−1h−1, which was 7.5 times as much as pristine CN and surpassed the performance of O-CN or K-CN. The enhanced CO2 reduction of K/O-CN was derived from its enlarged surface area and pore volume, magnified CO2 adsorption capacity, and narrowed band gap with better visible light absorption. The dual-doping of K and O accelerated the charge separation and reinforced reduction potential with a more negative conduction band. DFT calculation reveals that dual-doping impeded charge recombination by increasing spatial distance between photoinduced electrons and holes and caused a kinetic preference for CO desorption.

Epitaxial-grafting strategy to boost inert hydroxide photocatalytic performance: A case study of SnOx-MgSn(OH)6

To utilize -OH on the inert hydroxides, a layer of photoactive SnOx was epitaxially grafted on MgSn(OH)6 (MgHS) by controlling the hydrothermal solution at ca. pH 4. SnOx shows a strong interaction with MgHS and acts as photoactive sites to provide photoinduced electrons (e−) and holes (h+), while the host provides a hydroxyl-rich surface to strengthen and sustain ∙OH-mediated degradation process. Furthermore, both the transferring of photoinduced h+ from SnOx to MgHS and the adsorption of benzene (C6H6) on MgHS were promoted by SnOx. The synergistic effect between SnOx and MgHS is responsible for the high and stable performance for abating bisphenol A solution and gaseous C6H6 exhaust. ∙OH and protonated O2− are the main active species. This work demonstrated that the epitaxial-grafting of photoactive metal oxides on a host hydroxide photocatalyst is a promising strategy to boost the photocatalytic performance of inert hydroxide photocatalysts for environmental remediation.

Construction of interfacial electric field via Bimetallic Mo2Ti2C3 QDs/g-C3N4 heterojunction achieves efficient photocatalytic hydrogen evolution

Exploiting photocatalysts with high interfacial charge separation efficiency remains a huge challenge for converting solar energy into chemical energy. Herein, a novel 0D/2D heterojunction is successfully constructed by using bimetallic Mo2Ti2C3 MXene Quantum Dots (Mo2Ti2C3 QDs) firmly immobilized on the surface of g-C3N4 nanosheet via an electrostatic self-assembly strategy. The Mo2Ti2C3 QDs/g-C3N4 exhibits an efficient and stable photocatalytic hydrogen production performance up to 2809 µmol g-1h−1, which is 7.96 times higher than pure g-C3N4 nanosheet, and prominently exceeding many reported photocatalysts. Besides, a prominent apparent quantum yield achieves 3.8% at 420 nm. The significant performance improvement derives from the giant interfacial electric field that formed between large interface contact areas, ensuring greatly efficient separation and transfer of the photogenerated carriers. Furthermore, the 0D/2D heterojunction possesses high-quality interfacial contact, which reduces the interfacial recombination of photoinduced electrons and holes, causing the quick electron transfer from the g-C3N4 to electron acceptor Mo2Ti2C3 QDs, thus enhancing the charge utilization. Kelvin probe force microscopy (KPFM) measurements and density functional theory (DFT) calculation comprehensively demonstrate that g-C3N4 modified by Mo2Ti2C3 QDs can modulate the electronic structure and prompt the establishment of the interfacial electric field, which consequently leads to efficient photocatalytic activity. This study adequately illustrates that constructing heterojunction interfacial electric fields based on MXene quantum dots is a prospective pathway to engineering high-performance photocatalytic platforms for solar energy conversion.

Copper oxide-anchored ZnO nanoflakes for the enhanced photocatalytic degradation performance and mechanistic investigations

An efficient CuO anchored ZnO nanoflakes were synthesized through facile wet chemistry method and the catalysts were well characterized using various sophisticated instruments. CuO nanoparticle incorporation was found to have a direct linear relationship with light absorbance. The degradation ability of the ZnO/CuO p-n junction was studied on the degradation of methyl orange. Under UV–Vis light illumination, the photocatalytic removal efficacy of methyl orange over CuO/ZnO p-n junction is up to 89%, which is greater than that of barecatalysts. The maximized photocatalytic degradation performance might be ascribed to the augmented visible light harvesting capacity and reduced the rate of photogenerated electron-hole pair recombination. The efficient photoinduced electron and hole pair charge separation upon excitation is aided by the effective formation of p-n junctions between ZnO and CuO. Based on the findings, a plausible photocatalytic mechanism for the as-synthesized CuO anchored ZnO nanoflake was proposed.

Triazine- and porphyrin-based donor-acceptor microporous conjugated polymers for enhanced photocatalytic hydrogen production activity

Donor-acceptor type conjugated microporous polymers (D-A CMPs) have recently gained popularity as active components for photocatalytic hydrogen evolution from water due to their ability to separate the photoinduced holes and electrons efficiently and vastly absorb visible light. However, creating a novel CMP photocatalyst with high photoconversion efficiency is still difficult. Porphyrins and triazines exhibit intriguing electrical and optical features. We present here the directed synthesis and photocatalytic activity in hydrogen generation of two donor-acceptor isostructural triazine- and porphyrin-based conjugated microporous polymers (H-Por-TPT and Zn-Por-TPT CMPs). Our data demonstrate that both CMPs have extremely high specific surface areas (around 650 m2 g−1) and thermal stabilities (Td10: equal to 629 °C with char yields equal to 76.18 wt%). Introducing a Zn atom into a porphyrin ring profoundly influences its optoelectronic properties and photocatalytic efficiency for hydrogen generation from water. Zn-Por-TPT CMP has one of the highest reported values for a D-A CMP, with a photocatalytic hydrogen evolution rate of 11450 μmol g−1 h−1 when exposed to visible light. In addition, the Zn-Por-TPT CMP is notable not just for increasing the rate of hydrogen generation but also for improving photocatalysis stability during prolonged irradiation for roughly 30 h. These CMPs may prove useful as organic photocatalysts in future photocatalytic H2 production from water applications.

CuO-ZnO nanocomposites-based thin films: Characterization, physical properties and sunlight photocatalytic degradation of organic pollutants

One of the most commonly employed techniques for boosting photocatalytic efficiency by separating photo-induced electrons and holes is the formation of heterojunctions. The photocatalytic activity of CuO-ZnO nanocomposites-based thin films was investigated in this work for the decomposition of a model pollutant, methylene blue (MB), under sunlight irradiation. The spray pyrolysis method was utilized to produce nano-sized pure CuO and ZnO thin films, as well as CuO-ZnO nanocomposite thin films with varied molar ratios (Cu:Zn 1:3, 1:1, and 3:1). The structural and optical properties of the prepared materials were carefully studied. Contact angle measurements were used to determine the samples' wetting properties. XRD and Raman spectra confirmed the hexagonal würtzite and cubic structures of ZnO and CuO crystals in the different heterostructures. SEM images demonstrated the growth and distribution of the grains, with some spherical or plate-like nanostructures. The composition of the synthesized nanocomposites is confirmed by EDX analysis. UV-Vis investigations indicate that the optical band gaps are considerably impacted by the composition of nanocomposites. PL measurements confirmed a large number of defects in the synthesized nanocatalysts. These data also reveal that the formation of p-n heterojunctions prevented photogenerated carriers from recombining. The photocatalytic activity of the prepared CuO-ZnO nanocomposites was found to be greater than that of individual semiconductors. A possible mechanism and involvement of radicals in photocatalytic dye degradation were also proposed. As a result, the produced nanocomposite thin films might be beneficial for environmentally friendly and energy-saving wastewater treatment.

Synthesis of mesoporous p-CuAl2O4/n-YVO4 heterojunction nanocomposites and their utilization as effective photocatalysts for hydrogen evolution

The photocatalytic H2 evolution processes have received great attention from the scientific society using semiconductor photocatalysts, and the main bottleneck for the newly synthesized photocatalyst is the swift recombination rate of photoinduced holes and electrons. In this contribution, heterojunction p-CuAl2O4/n-YVO4 photocatalyst was synthesized through the facile sol–gel process utilizing the block copolymer templating. The photocatalytic ability and stability of the p-CuAl2O4/n-YVO4 heterojunction photocatalysts have been examined by H2 evolution in glycerol solution as a hole scavenger under visible illumination. TEM and XRD analyses indicated the formation of YVO4 (5–10 nm) with a tetragonal structure and their uniform interaction with spinel-type CuAl2O4 (5 nm). The CuAl2O4/YVO4 nanocomposites were verified for the first time to be competitive photocatalysts for H2 evolution compared with bare YVO4 NPs. At optimum conditions, the 15 % CuAl2O4/YVO4 nanocomposite revealed an enhanced H2 evolution rate (2994.6 µmolg-1h−1), about 72.5-fold that of bare YVO4 NPs (41.3 µmolg-1h−1). The heterojunction interface of p-CuAl2O4/n-YVO4 NPs was constructed according to their band structures to build S-scheme mechanism. The photoelectrochemical and PL measurements of the CuAl2O4/YVO4 photocatalysts are systematically examined to confirm our photocatalytic H2 evolution studies. It revealed that introducing CuAl2O4 on YVO4 effectively inhibited the recombination of photocarriers, thus promoting the H2 evolution rate. The work provides advantages for plausible designing p-n heterostructures and exhibits new insight to promote photocatalytic performance for potential applications.

A co-precipitation synthesized BiOI/(BiO)2CO3 nanocatalyst: An experimental design and mechanism study towards photodegradation of sulfasalazine

BackgroundIncreased antibiotic consumption residues a large amount of antibiotics in the bacterial communities and ecosystems, leading to bacterial persistence against them. Thus, in recent decades, an urgent need has been to introduce/develop novel catalysts/adsorbents/methods to diminish the pollution extent of the aquatic environment by various organic pollutants like antibiotics. MethodsBiOI/(BiO)2CO3 was synthesized by adding ammonium iodide to the aqueous suspension of (BiO)2CO3 (BOC) under hydrothermal conditions. The individual BiOI and (BiO)2CO3 and their p-n heterojunction system were characterized by some identification techniques like UV–vis diffuse reflectance spectroscopy (DRS) and electrochemical impedance spectroscopy (EIS). Significant findingsThe direct band gap energies of 1.99, 3.54, and 2.42 eV were obtained for BiOI, (BiO)2CO3, and BiOI/(BiO)2CO3 samples from the Tauc plots. Both CVs and EIS results confirmed better charge transfer in the coupled catalyst. pHpzc for BiOI, (BiO)2CO3 and BiOI/(BiO)2CO3 was 6.3, 10.1, and 6.5. The response surface methodology (RSM) approach was used to construct a design model to investigate the interaction effects of the most influencing variables on the boosted catalytic effect of the coupled catalyst toward sulfasalazine (SSZ) as a model antibiotic pollutant. The model goodness was confirmed based on model F-value=20.59 > F0.05, 14, 13 = 2.55 and lake of fit (LOF) F-value = 0.364 < F0.05, 10, 3 = 8.73, as well as by adequate regression coefficient (R2) of 0.9705, adjusted R2 (0.9699), and predicted R2 (0.9575) values. RSM optimal run included pH 6.0, catalyst dose: 0.55 g/L, irradiation time: 50 min, and SSZ concentration of 6 ppm, which resulted in a 95.3 % photodegradation efficiency. The relative role of photoinduced holes> photoinduced electrons > hydroxyl radicals> superoxide radicals was obtained in the photodegradation efficiency by the results obtained in the presence of some scavenging species. Accordingly, the photodegradation pathway was suggested. We believe simple preparation of the BiOI/(BiO)2CO3 photocatalyst via a co-precipitation anion-exchanged consisted procedure by adding iodide anion to the aqueous suspension of (BiO)2CO3 is an advantage of this work.

Accelerated electron and mass transfer through constructing H2WO4/Ti3C2/g-C3N4 Z-scheme photocatalyst for environmental remediation

The catalytic efficiency of photocatalysts highly depends on electron transport and mass transfer. Herein, we designed and prepared an effective H2WO4/Ti3C2/g-C3N4 (HTC) Z-scheme heterojunction through interfacial engineering strategy. The results manifested that 97.4% of Cr(VI) (80 μM, 50 mL) could be removed by HTC heterojunction within 10 min under visible light irradiation. The reduction rate constant of Cr(VI) for H2WO4/g-C3N4 (HC) heterojunction increased by a factor of 21 after introducing the conductive Ti3C2. Moreover, 96% of tetracycline (TC, 10 mg L−1, 50 mL) could be degraded by HTC heterojunction within 30 min. The electronic conductivity and ionic diffusion coefficient of HC heterojunction increased by a factor of 64 and 1064 after adding Ti3C2, respectively. This result indicated that the introduction of highly conductive Ti3C2 significantly improved the electron and mass transfer of the heterojunction. Meanwhile, the HCT heterojunction displayed favorable photocurrent, and keep excellent photostability during the long-term test. Moreover, density functional theory (DFT) calculations demonstrated that the internal electric field (IEF) from g-C3N4 to H2WO4 in HCT heterojunction promotes the combination of the photoinduced electrons in the H2WO4 conduction band (CB) with photoinduced holes in the g-C3N4 valence band (VB), thus accelerating the charge transfer in the HCT Z-scheme heterojunction. The antibacterial efficiency of HTC heterojunction against E. coli and S. aureus could reach up to 98.4% and 99.7%, respectively. The degradation intermediates and the potential degradation mechanism of TC were analyzed and proposed based on the results of HPLC-MS analysis. Moreover, the toxicity of TC and degradation intermediates were estimated by Toxicity Estimation Software (T.E.S.T.) based on quantitative structure-activity relationship (QSAR). This work provided a valuable guideline for designing the effective MXene-based Z-scheme heterojunction for environmental remediation.

Embedding Carbon Quantum Dots into Crystalline Polyimide Covalent Organic Frameworks to Enhance Water Oxidation for Achieving Dual-Channel Photocatalytic H2O2 Generation in a Wide pH Range.

Photocatalytic technique is regarded as the cleanest approach for producing H2O2. Herein, two kinds of novel polyimide COFs decorated with CQDs (namely, MPa-COFs/CQDs and MNd-COFs/CQDs) were constructed by using the one-pot hydrothermal method. Due to the electron donor role of CQDs, the recombination of photoinduced electrons and holes was suppressed after the combination of polyimide COFs with CQDs. Importantly, the introduction of CQDs not only boosted the absorbing ability of polyimide COFs toward visible light but also reduced the impedance and improved the charge transfer efficiency. After CQDs were embedded into polyimide COFs, the surface hydrophilicity of catalysts was significantly improved, which provided convenience for the water oxidation reaction. Benefiting from the electron donor-acceptor interaction between polyimide COFs and CQDs, a step-by-step two-electron oxygen reduction reaction over polyimide COFs was enhanced. More interestingly, the embedding of CQDs can create a direct two-electron water oxidation reaction pathway, which played an important role in photocatalytic H2O2 generation. Meanwhile, H+ generated from water oxidation can also be used for the reduction of oxygen to form H2O2. Under the synergistic effects of water oxidation and oxygen reduction, as-prepared MPa-COFs/CQDs-2 displayed excellent performance in photocatalytic H2O2 generation, and its yield was as high as 540 μmol/g within 60 min. In short, the current work shared an effective strategy to improve the performance of polyimide COFs in photocatalytic H2O2 production.

First fluorine doping of In2O3 films and its crucial role in enhancing photocatalytic activity

We prepared In2O3 film on the wire mesh of stainless steel by a facile hydrothermal method followed by annealing. To enhance the visible-light-responsive photocatalytic activity of the prepared In2O3 film, we in-situ doped the element fluorine by adding FTO glass as the fluorine source during the hydrothermal process. The prepared In2O3 and F-doped In2O3 films were characterized by XRD, SEM, HRTEM, XPS, UV–vis spectra, PL, and electrochemical measurement. The results show that In2O3 octagonal pyramids of cubic phase were formed. The fluorine doping promoted to growth of In2O3 pyramids and porous In2O3 pyramids help to adsorb RhB dye molecules. Beside, the fluorine doping introduced a new impurity level between the VB and CB of In2O3, thereby, decreasing the bandgap value from 2.84 to 2.60 eV. As a result, it extended the visible light absorption range and more photoinduced electrons and holes can be excited under simulated sunlight. Moreover, the doping inhibited the recombination of photogenerated carriers. It is worth noting that the fluorine doping changed the surface state of In2O3 and enhanced the chemical adsorption of dissociated oxygen species. It finally made RhB dye molecules strongly adsorbed the surface of F-doped In2O3 film. The photocatalytic activity of the F-doped In2O3 film was increased by 7.6 times compared with the pristine In2O3 film because of the combined action of the above reasons. The importance of active groups for RhB photodegradation is O2•− > h+ > e− > •OH.

Ag Nanoparticles-decorated p-type CuO/n-type ZnO heterojunction nanofibers with enhanced photocatalytic activities for dye degradation and disinfection

With the rapid development of industry, organic pollutants and bacterial contamination in water resources are becoming increasingly severe. Photocatalysis is an effective approach to address this problem. ZnO, as a traditional n-type semiconductor photocatalyst, has a relatively wide bandgap, which results in a narrow range of light absorption and quick recombination of photogenerated charge carriers, thus limiting its development. In this work, we constructed p-type CuO/n-type ZnO heterojunction nanofibers (HNFs) to extend the light harvesting range and improve the migration and separation of the photoinduced electrons and holes across the hetero-interface through. Afterwards, Ag nanoparticles were introduced into above HNF matrix to reinforce the photocatalytic activity. Results showed that, upon simulated sunlight irradiation, the Ag NPs-decorated p-type CuO/n-type ZnO HNFs exhibited enhanced photocatalytic activities. After 20 min of simulated sunlight irradiation, approximately 98.5% of MB was degraded by 1.0 at% Ag NPs-decorated p-type CuO/n-type ZnO HNFs. Additionally, after 10 min of irradiation, the disinfection efficiency of HNFs for Escherichia coli was > 99.99%. It is worth noting that this study has opened up a new pathway for the rational design of p-n junction photocatalysts with superior charge transfer properties, to achieve remarkable photocatalytic disinfection and degradation activities.

Bifunctional Lewis acid-base nanocatalysts with dual active sites for strengthened coupling of alcohol conversion and H2 evolution

The synergistic of organic transformation with H2 production in one redox cycle is highly desirable to achieve the full use of photogenerated holes and electrons but challenging. Herein, Lewis acid-base nanocatalysts in which Ni decorated defective ZnIn2S4 (denoted as Ni/VZIS) has been prepared through photodeposition with Zn defective ZnIn2S4 nanosheets as precursor. The Zn vacancies favors the selective deposition of Ni, enabling the co-exposure of Lewis acid Ni and Lewis base S adjacent dual active sites. In-situ FTIR results reveal the coexistence of Ni and Zn vacancy on ZnIn2S4 favored the chemisorption of benzyl alcohol. The electron-deficient Ni Lewis acid (LA) site and electron-rich S Lewis base (LB) site can act as benzyl alcohol conversion and H2 evolution sites, respectively, thus facilitating the full use of photoinduced electrons and holes. The spectroscopy and photoelectrochemical studies demonstrate the transfer and separation of photogenerated carries are also facilitated in the nanohybrids. As such, the Ni/VZIS photocatalyst show outstanding performance of photocatalytic conversion benzyl alcohol (BA) into benzaldehyde (BAD) and H2, with the optimal H2 generation rate of 81.9 μmol h−1, accompanying benzaldehyde generation rate of 73.7 μmol h−1. This work provides a profound insight into the designing of multi-functionalized nanohybrids for the full use of photoexcited electrons-holes pairs.

Evaluating a Second Time Scale for Hole Extraction in an Actual Photocatalytic Reaction: The Method.

Photoinduced hole extraction, which is widely believed to occur on the picosecond-nanosecond time scale, exhibits sensitive correlation with semiconductor-cocatalyst interfacial electron transfer that occurs on a second time scale in a photocatalytic reaction. This inherent correlation means that the required high density of electrons for overcoming the potential barrier severely suppresses the survival and interfacial extraction of photogenerated holes. We here propose to evaluate the time constant for the occurring hole extraction by separately monitoring the rise and decay of the photoinduced potential. The evaluated second time scale indicates that hole extraction crucially influences the actual photocatalytic reaction. To improve photocatalytic photon utilization, we facilitate hole extraction by lowering the semiconductor-cocatalyst contact barrier.

Realization of multilocal gradient-doping PCN by alkali metal ion sustained release capsules for enhanced photocatalytic water splitting

The gradient-doping technique has been widely applied to induce an oriented built-in electric-field. However, it is still not efficient enough for charge mobility especially for particulate semiconductors, as the field is primarily in one direction from inner to surface. Here, we propose a multilocal gradient-doping technique that a nano-capsule is designed to store dopants and then release them into semiconductors nonuniformly. As an illustration, scattered pyrochlore-type K2Ta2O6 nanoparticles have been validated the capability of storing and releasing K+, which subsequently diffuse into the substrate PCN. Multi point-radiative gradient in K+ concentration, confined within the K2Ta2O6’s vicinity, will construct several 3D potential wells which can not only accelerate the carrier separation but also offer more migration channels for both photo-induced electrons and holes to the surface. Consequently, the multilocal K+ gradient-doping PCN shows the longest carriers’ lifetime and highest AQY (∼21.8% at 400 nm) compared with the other uniformly doping techniques.

Construction of S-scheme heterojunction WO3/Bi2O4 with significantly enhanced visible-light-driven activity for degradation of tetracycline

Recently, S-scheme heterojunctions have drawn much attention due to their unique interface charge transfer pathway and resultantly excellent photocatalytic performance. Herein, a novel 2D/1D S-scheme heterojunction photocatalyst was constructed by loading WO3 nanosheets on the surface of rod-shaped Bi2O4. The S-scheme charge transfer mechanism between WO3 and Bi2O4 was affirmed by the results of the Fermi level and in situ irradiated X-ray photoelectron spectroscopy (XPS). The construction of the S-scheme heterostructure significantly accelerated the separation and migration of the photoinduced electrons and holes in WO3/Bi2O4 and preserved the photogenerated holes and electrons with high redox capability in the valence band of WO3 and the conduction band of Bi2O4. Compared to the pristine WO3 and Bi2O4, the heterojunction WO3/Bi2O4 exhibits significantly boosted activity for the degradation of tetracycline (TC) under visible-light irradiation. The photodegradation efficiency of TC is up to 90 %. The degradation rate constant (0.0587 min−1) for WO3/Bi2O4 toward TC is 2.21 and 28.34 times those for Bi2O4 and WO3. The improved activity of WO3/Bi2O4 is attributed to S-scheme interfacial charges migration pathway, unique 2D/1D heterostructure and exceptional visible light absorption ability. Additionally, WO3/Bi2O4 shows good photochemical stability and acid-alkali suitability. The common inorganic ions and humus (fulvic acid) in natural water have little influence on the photodegradation of TC. This work brings a new idea for constructing heterojunction photocatalysts with high activity for boosted TC photodegradation.

Effect of UV Irradiation on the Alternating Wet and Dry Corrosion Behavior of Galvanized Steel in Sodium Chloride Solution

In this paper, the corrosion performance of galvanized steel was investigated in a simulated marine environment, under UV irradiation coupling with an alternating wet and dry cycle in a NaCl solution. The surface morphology, composition, and corrosion performance of galvanized steel before and after different alternating wet and dry corrosion under UV irradiation were investigated. The results show that the corrosion current density gradually increases and the corrosion resistance decreases as a function of the alternating wet and dry corrosion cycles. Meanwhile, UV irradiation accelerates the increase in the corrosion current density and the decrease in the corrosion resistance. In addition, the corrosion product ZnO shows a semiconductor property, and the photo-induced electrons and holes produced under UV can participate in the corrosion reaction and promote the formation of loose corrosion products Zn(OH)2, Zn5(OH)8Cl2, and Al2Cl3(OH)5·4H2O, thus accelerating the corrosion of galvanized steel in the atmosphere environment.

A Novel MoS2/TiO2/Graphene Nanohybrid for Enhanced Photocatalytic Hydrogen Evolution under Visible Light Irradiation

Graphene is regarded as a potential co-photocatalyst for photocatalytic hydrogen (H2) evolution, but its great photocatalytic ability requires tuning the band gap structure or design morphology of composites. In this study, MoS2/TiO2/graphene (MTG) nanohybrids were fabricated at varied ratios of graphene and served as co-photocatalysts for H2 evolution. The results exhibited that the H2 evolution of MTG-10 obtained is much better than others. The amount of hydrogen evolution was high, which was found to be 4122 μmol g−1 of H2 in 5 h with photocatalytic systems, which is almost 7.5~13.4 times greater than that of previous pristine MoS2 (548 μmol g−1) and TiO2 (307 μmol g−1) samples, respectively. This is significantly attributed to the graphene as a bridge of MoS2/TiO2 and the incorporation of graphene, suggesting the synergistic effect of the rapid electron-transferring of photoinduced electrons and holes and the powerful electron-collecting of graphene, suppressing the charge recombination rate.

Self-polarized schorl optimizing TiO2 for photocatalytic persulfate activation and organic pollutants degradation

Photocatalytic activation of persulfate has exhibited tremendous potential in water purification because of its green and environmentally friendly process. However, this process often exhibits low activation efficiencies and difficult recovery of the photocatalyst. Herein, schorl-supported nano-TiO2 composite photocatalysts (S/TiO2) were prepared by a mechanical grinding method for efficient activation of potassium monopersulfate (PMS). The anatase TiO2 nanoparticles with particle size of approximately 30 nm was uniformly loaded on the surface of schorl via forming Si-O-Ti bonds. The S/TiO2 assisted with PMS (S/TiO2-PMS) exhibited remarkable degradation performance and stability. In this system (S/TiO2-PMS), the C/C0 value of phenol solution (10 ppm) were decreased to 0.070 and 0 after 30 min and 90 min of irradiation, where the degradation extent were 93.0% and 100% respectively. The rate of phenol degradation with S/TiO2-PMS was 12.6 times that seen with TiO2-PMS. The oxidation active species were holes and SO4•− in S/TiO2-PMS system subjected to simulated sunlight. It was demonstrated that the polarization electric field of the schorl enhanced the separation efficiency of the photoinduced electrons and holes for improving the performance of the S/TiO2-PMS. On the other hand, the transformations of Fe3+ and Fe2+ on the schorl surface further promotes the activation of PMS. This work provides a new choice for designing TiO2-based photocatalytic persulfate activation system targeting the field of advanced oxidation water treatment.