Photocatalytic Reduction Activity Research Articles

A wide visible light active photocatalyst Mg5Ta4O15-xNy for water oxidation and reduction

More than 1.6 eV band gap reductions have been realized on Mg5Ta4O15 by nitrogen doping with its pseudobrookite structure maintained. The nitrogen doped Mg5Ta4O15, i.e. Mg5Ta4O15-xNy, shows broad absorption in the visible light region and promising photocatalytic activity for both water reduction and oxidation reactions under visible light illumination (λ ≥ 400 nm). Apparent quantum efficiency as high as ~0.90% has been achieved at 420 ± 20 nm on Mg5Ta4O15-xNy which is comparable to a number of active metal oxynitrides photocatalysts. Apart from visible light absorption, Nitrogen doping on Mg5Ta4O15 is also accompanied by improved surface hydrophilicity and a negative shift of flat band potential. This simple strategy for band gap engineering can be extended to other metal oxides which may open new playgrounds in the design and development of efficient visible light active photocatalysts.

Enhanced photocatalytic reduction activity of BiOCl nanosheets loaded on β-Bi2O3

BiOCl nanosheets were loaded on the surface of β-Bi2O3 and its photocatalytic reduction activity was investigated. The composite displays excellent photocatalytic reduction activity. The NH3 yield rate of β-Bi2O3/BiOCl composite is nearly 25 times as that of pure BiOCl under Xenon lamp irradiation. The β-Bi2O3/BiOCl heterojunction presents superior photocatalytic reduction activity for the degradation of Cr(VI) ions, and Cr(VI) ions are totally removed in 18 min. The results of photocurrent and electrochemical impedance spectroscopy measurements reveal that the formation of β-Bi2O3/BiOCl heterojunction contributes to reduce the recombination of the photogenerated electrons and holes. The process of photocatalytic reduction activity over composite is explained by Z-scheme mechanism.

A Covalent Triazine-Based Framework Consisting of Donor-Acceptor Dyads for Visible-Light-Driven Photocatalytic CO2 Reduction.

Photocatalytic conversion of CO2 into value-added chemical fuels is a promising approach to address the depletion of fossil energy and environment-related concerns. Tailor-making the electronic properties and band structures of photocatalysts is pivotal to improve their efficiency and selectivity in photocatalytic CO2 reduction. Herein, a covalent triazine-based framework was developed containing electron-donor triphenylamine and electron-acceptor triazine components (DA-CTF). The engineered π-conjugated electron donor-acceptor dyads in DA-CTF not only optimized the optical bandgap but also contributed to visible-light harvesting and migration of photoexcited charge carriers. The activity of photocatalytic CO2 reduction under visible light was significantly improved compared with that of traditional g-C3 N4 and reported covalent triazine-based frameworks. This study provides molecular-level insights into the mechanism of photocatalytic CO2 reduction.

Switching on wide visible light photocatalytic activity over Mg4Ta2O9 by nitrogen doping for water oxidation and reduction

Band gap engineering on wide band gap semiconductor photocatalysts is of critical significance in improving their solar energy utilization. Here, we have successfully realized large band gap reduction and visible light photocatalytic water splitting on a wide band gap semiconductor Mg4Ta2O9 by nitrogen doping. More than 2.6 eV reductions in band gap have been achieved after doping nitrogen into Mg4Ta2O9, which strikingly red-shifts its absorption edge from less than 300 nm to as far as 600 nm. The nitrogen doped Mg4Ta2O9, i.e. Mg4Ta2O9-xNy, shows promising photocatalytic activities for water reduction and oxidation under visible light illumination (λ ≥ 400 nm). Apparent quantum efficiency as high as ∼1.57% has been achieved at 420 ± 20 nm which is comparable to a number of active metal oxynitride photocatalysts. Photoelectrochemical analysis suggests that this band gap reduction stems mainly from an uplift of valence band edge position along with nitrogen doping. Our band gap engineering on a compact corundum type compound implies that nitrogen doping can be applicable to a wider range of metal oxides, not necessarily limited to those with an ‘open’ crystal structure (tunnels or layers, etc.) reported in the literatures, thereby opening new possibilities in searching and developing visible light active photocatalysts.

Non-noble metal thickness-tunable Bi2MoO6 nanosheets for highly efficient visible-light-driven nitrobenzene reduction into aniline

High efficiency and selectivity is significant for photocatalytic organic transformation. In this work, the efficient photocatalytic reduction of nitrobenzene into aniline is achieved on non-noble metal thickness-tunable bismuth molybdate nanosheets prepared by the simple hydrothermal reaction. The photocatalytic activity of Bi2MoO6 strongly depends on the nanosheet thickness. The Bi2MoO6 monolayer displays remarkably enhanced photocatalytic activity for selective reduction of nitrobenzene than bilayer, multilayers and bulk Bi2MoO6 due to the unique properties of 2D materials with the large fraction of surface atoms and the ultrafast charge separation. The obtained conversion rate of 487.5 μmol g−1. h-1 (>95% conversion and >99% selectivity within 60 min reaction) on Bi2MoO6 monolayers is 5 times higher than that of Bi2MoO6 bulk, far exceeding most of common photocatalysts up to date. This work provides a thickness dependent nanosheet concept in the design of newly highly efficient catalysts for the photocatalytic reduction conversion of nitroarenes to anilines.

InVO4/β-AgVO3 Nanocomposite as a Direct Z-Scheme Photocatalyst toward Efficient and Selective Visible-Light-Driven CO2 Reduction.

Photocatalytic CO2 reduction to solar fuel is a promising route to alleviate the ever-growing energy crisis and global warming. Herein, to enhance photoconversion efficiency of CO2 reduction, a series of direct Z-scheme composites consisting of β-AgVO3 nanoribbons and InVO4 nanoparticles (InVO4/β-AgVO3) are prepared via a facile hydrothermal method and subsequent in situ growth process. The prepared InVO4/β-AgVO3 composites exhibit enhanced photocatalytic activity for reduction of CO2 to CO under visible-light illumination. A CO evolution rate of 12.61 μmol·g-1·h-1 is achieved over the optimized 20% In-Ag without any cocatalyst or sacrificial agent, which is 11 times larger than that yielded by pure InVO4 (1.12 μmol·g-1·h-1). Moreover, the CO selectivity is more than 93% over H2 production from the side reaction of H2O reduction. Significantly, based on the results of electron spin resonance (ESR) and in situ irradiated XPS tests, it is proposed that the synthesized InVO4/β-AgVO3 catalysts comply with the direct Z-scheme transfer mechanism. Significantly improved photocatalytic activities for selective CO2 reduction could be primarily ascribed to effective separation of photoinduced electron-hole pairs and enhanced reducibility of photoelectrons at the conduction band of InVO4. This work provides a new insight for constructing highly efficient photocatalytic CO2 reduction systems toward solar fuel generation.

Atomic-level insights in tuning defective structures for nitrogen photofixation over amorphous SmOCl nanosheets

Direct fixation of N2 at room temperature by photocatalysis is the most intriguing process toward sustainable production of ammonia, where chemisorption of inert N2 and delivery of photogenerated electrons to NN bond are recognized bottlenecks. Here, we develop a catalyst of amorphous SmOCl nanosheets (A-SmOCl) with remarkable activity for photocatalytic reduction of N2. Impressively, the ammonia production rate of A-SmOCl reached 426 μmol·gcat.−1·h−1 under light irradiation in water without any sacrificial agents. Moreover, A-SmOCl exhibited an apparent quantum efficiency of 0.32% at 420 nm. Further mechanistic studies revealed that the existence of abundant oxygen vacancies in A-SmOCl significantly improved the adsorption and activation of N2. Meanwhile, the enhanced Sm–O covalency promoted the delivery of photogenerated electrons to chemisorbed N2, contributing to the superior catalytic activity of A-SmOCl.

MOF-based In2S3-X2S3 (X = Bi; Sb)@TFPT-COFs hybrid materials for enhanced photocatalytic performance under visible light

A novel catalytic material of MOF-based In2S3-X2S3 (X = Bi; Sb)@TFPT-COFs hybrids was designed and synthesized by using an interface ion-exchange method with MOFs as the precursors. The hybrid materials were fabricated by combining heterojunctions with TFPT-COFs through CN bonds. The functionalization of the amino groups on the heterojunction surface was a crucial step to construct the MOFs@COFs hybrid materials. The resulting samples were hierarchical tubular nanostructures with uniform nano-scale interfacial contacts. The doping of Bi3+ or Sb3+ further facilitated the construction of heterojunctions to reduce the band gap value of In2S3 and extended light absorption range. The synergistic effect between the frameworks contained in In2S3-X2S3 (X = Bi; Sb) and the triazine frameworks of TFPT-COFs was conducive to accelerating charge transportation and separation. The photo-erosion of heterojunctions could also be prevented by the encapsulated TFPT-COFs sheets. Noteworthily, the photocatalytic degradation abilities of hexavalent chromium, ponceau-4R and rhodamine B were significantly improved after the introduction of TFPT-COFs. Especially, In2S3-Sb2S3@TFPT-COFs performed excellent photocatalytic reduction activity. Approximately 100% of aqueous Cr(VI) was photo-reduced within only 5 min. Based on the experimental results of UV–Vis adsorption spectra and ESR spectra, a possible mechanism was proposed to explain the excellent photocatalytic performance of the photocatalytic system.

Dual II Heterojunctions Metallic Phase MoS2 /ZnS/ZnO Ternary Composite with Superior Photocatalytic Performance for Removing Contaminants.

Fabricating a high-performance photocatalyst to efficiently solve serious environmental problems is an urgent affair. Herein, a series of MoS2 /ZnO composites were successfully fabricated through a facile hydrothermal route using Na2 MoO4 , (NH2 )2 CS and urchin-like ZnO as precursors. According to the results of XRD and XPS, it was found that ZnS appeared in MoS2 /ZnO composite; meanwhile, the content was positively correlated with the weight of the precursor (NH2 )2 CS. It should be noted that the morphology and the metallic phase content of MoS2 grown in situ on the surface of ZnO were affected by the molar ratio of Na2 MoO4 and ZnO. Benefiting from the special dual II heterojunctions of MoS2 /ZnS/ZnO ternary composite, the material exhibited excellent charge separation and transfer performances. In the photocatalytic measurements, the MoS2 /ZnS/ZnO (Na2 MoO4 :ZnO 1:2 MZ2) composite not only exhibits excellent photocatalytic CrVI reduction activity of 42.3×10-3 min-1 , but also displays remarkable adsorption performance (nearly 32.1 %) for Cr2 . In addition, the ternary composite shows dominant photocatalytic CrVI reduction activities compared to other photocatalysts. This work provides a high-efficient MoS2 /ZnS/ZnO ternary photocatalyst for environmental treatment.

Preparation of SnO2/conjugated polyvinyl alcohol derivative nanohybrid with good performance in visible light-induced photocatalytic reduction of Cr(VI)

A new visible light-responsive SnO2/conjugated polyvinyl alcohol derivative (CPVA) nanohybrid photocatalyst was prepared by an easy-to-implement three-step method, using low cost and easily accessible SnCl4·5H2O, PVA and H2O as the source materials. The photocatalytic properties of the as-prepared SnO2/CPVA nanohybrid were examined through the reduction of aqueous Cr(VI) in the presence of citric acid and visible light (λ > 420 nm). The compositional and structural analysis of SnO2/CPVA nanohybrid after the recycle stability test was also performed. The photodegradation efficiency of Cr(VI) using SnO2/CPVA nanohybrid and other reported visible light-responsive photocatalysts (g-C3N4 and ZnFe2O4/CPVC nanocomposite) were compared. Besides, the effects of the solution pH and different water matrices (including black chromium electroplating solution, industrial cooling water, yellow sea water, and tap water) on the efficiency of photocatalytic reduction of Cr(VI) by SnO2/CPVA nanohybrid were also investigated. The results manifested that the as-prepared SnO2/CPVA nanohybrid had both high activity and good stability in photocatalytic reduction of aqueous Cr(VI) under visible light irradiation. According to the results of photoabsorption, photoluminescence, transient photocurrent response, electrochemical impedance, and Mott-Schottky characterization, it was deduced that the notable visible light-activated photocatalysis of SnO2/CPVA nanohybrid may originate from its prominent visible light-absorbing ability and the efficient electron transfer from CPVA to SnO2 (which results in the efficient separation of photoinduced charge carriers of CPVA as well as the sensitization of SnO2).

Visible light induced photocatalytic reduction of Cr(VI) by self-assembled and amorphous Fe-2MI

Visible-light-active Fe-2MI assemblies were prepared at room temperature using 2-Methylimidazole (2MI) as organic ligand to form complex with Fe(II) or Fe(III). TGA and XRD characterizations indicated that Fe(II) can form more stable complex and higher coordinating percentage with 2MI relative to Fe(III). Besides, Fe(II)-2MI displayed amorphous state with larger BET surface area and higher photocurrent response. At very low catalyst dosage (0.1 g/L), highest activity for Cr(VI) reduction can be achieved using Fe(II)-2MI as photocatalyst. The estimated pseudo-first-order rate constant (0.021 min−1) was 1.4 and 2.1 times that on Fe(III)-2MI and Fe(II)-NaOH, respectively. The well-known ZIF-67 (Co-2MI), ZIF-7 (Zn-2MI) and Fe-MOFs with other organic ligands (H2BDC, NH2-H2BDC or FA) were also used as control samples. Optimal activity for photocatalytic reduction of Cr(VI) was achieved by Fe(II)-2MI. The operating factors was optimized at acidic pH (2.0), higher catalyst dosage (0.3 g/L) and appropriate concentration of coexisting organics (2.0 mM) within the tested range. The stability of Fe(II)-2MI was investigated at different pH values (2, 3 and 4.64), which all displayed good stability. Mechanism study indicated that Fe(II)-2MI has adequate conduction and valence band positions for Cr(VI) reduction and organics oxidation, respectively. Therefore, the as-prepared amorphous Fe(II)-2MI assemblies may be cheap, stable and easy available candidate for the photocatalytic disposal of Cr(VI)-containing wastewaters.

Infrared studies of surface carbonate binding to diimine-tricarbonyl Re(I) and Mn(I) complexes in mesoporous silica

Diimine-tricarbonyl Re(I) and Mn(I) complexes have demonstrated interesting activity in photocatalytic and electrochemical CO2 reduction. In this study, we take a surface chemistry approach to investigate interactions of CO2 with Re(I) and Mn(I) complexes in the presence of triethylamine. The molecular complexes were adsorbed on the surface of a mesoporous silica. Under dark conditions, formation of metal-carbonate adducts was observed by infrared spectroscopy in the presence of CO2, triethylamine, and surface silanol groups. The Langmuir adsorption model was utilized to extract quantitative information regarding surface carbonate binding to the two molecular complexes. The results indicate that binding of carbonate was much stronger on the Re(I) center than on Mn(I), consistent with prior observations regarding the relative activities of these complexes in CO2-reduction catalysis.

Oxygen Vacancy Generation and Stabilization in CeO2–x by Cu Introduction with Improved CO2 Photocatalytic Reduction Activity

Introducing O vacancies into the lattice of a semiconductor photocatalyst can alter its intrinsic electronic properties and band gap, thus enhancing the visible light absorption, promoting the sepa...

Separation of hot electrons and holes in Au/LaFeO3 to boost the photocatalytic activities both for water reduction and oxidation

Abstract Construction of plasmon-based nanostructures is an effective way to enhance the photocatalytic activities of semiconductor photocatalysts for water-splitting. However, the synergistic effect of plasmon-related hot electrons and holes for water splitting in the plasmon-hybrid photocatalyst is rarely considered. Herein, we construct a plasmon-based Au/LaFeO3 composite photocatalyst to investigate the complex roles of hot electrons and holes for solar water splitting. Benefiting from the formation of Schottky junction and surface plasmon resonance effect of the Au nanoparticles, the synthesized photocatalyst exhibits an excellent photocatalytic activity for each half-reaction of water splitting, and the rates for H2 and O2 generation are obtained as high as 202 μmol g−1 h−1 and 23 μmol g−1 h−1, respectively. Moreover, an in-depth investigation reveals that the improved hydrogen evolution is caused by the hot electron injection from Au to LaFeO3, and the hot holes in Au induced by the separation of hot charges can initiate the water oxidation directly on the surface of gold. Thus, this work provides a new insight into the synergistic effect of plasmon-related hot electrons and holes for boosting the photocatalytic reactions.

Photocatalytic CO2 reduction activity of Z-scheme CdS/CdWO4 catalysts constructed by surface charge directed selective deposition of CdS

Rational construction of Z-scheme photocatalysts and deep exploration of Z-scheme transfer mechanism are highly desirable for improving the activity of CO2 reduction photocatalysts but remains a significant challenge. Herein, we synthesized a series of heterostructured CdS/CdWO4 materials by selectively depositing CdS nanoparticles on the edges of CdWO4 nanoplates. Selective deposition mechanism of CdS and the formation of the composites were studied in detail. The photocatalytic CO2 reduction activities of the synthesized materials were investigated and the results show that CdS/CdWO4 materials exhibit higher photocatalytic activity than pure CdS and CdWO4. We suggest that the enhanced photoreduction CO2 activity is attributed to Z-scheme charge transfer mechanism based on the analyses of the products of CO2 reduction and the band structure of CdS and CdWO4. Kelvin probe force microscope on CdWO4 nanoplates shows that the photogenerated electrons, driven by electric field forces, would migrate to the edge of CdWO4. The charge transfer direction, coupling with the selective deposition of CdS nanoparticles, facilitates CdS/CdWO4 composites following Z-scheme transfer. In-situ Pt photodeposition tests provide strong experimental support to the charge transfer mechanism. The results gained herein are expected to provide some useful insights into the structure-oriented rational design of Z-scheme photocatalysts for CO2 reduction.

One-Step Synthesis of MoS2/TiSi2 via an In Situ Photo-Assisted Reduction Method for Enhanced Photocatalytic H2 Evolution under Simulated Sunlight Illumination

A new MoS2/TiSi2 complex catalyst was designed and synthesized by a simple one-step in situ photo-assisted reduction procedure. The structural and morphological properties of the composites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and ultraviolet-visible diffused reflectance spectroscopy (UV-vis DRS), which proved the formation of MoS2/TiSi2. MoS2/TiSi2 with optimized composition showed obviously enhanced photocatalytic activity and superior durability for water reduction to produce H2. The H2 generation rate over the MoS2/TiSi2 photocatalyst containing 3 wt % MoS2 reached 214.1 μmol·h−1·g−1 under visible light irradiation, which was ca. 5.6 times that of the pristine TiSi2. The improved photocatalytic activity of MoS2/TiSi2 could be related to the broad response spectrum, large visible light absorption, and synergies among MoS2 and TiSi2 that enhance photoexcited charge transfer and separation.

The MoS2/TiO2 heterojunction composites with enhanced activity for CO2 photocatalytic reduction under visible light irradiation

The MoS2/TiO2 heterojunction composites photocatalysts exhibits excellent photocatalytic performance, and they were resoundingly synthesized by a one-step hydrothermal experimental method combined with mild calcination (300 °C) under an argon atmosphere. Under the visible light irradiation, the photocatalytic activity of MoS2/TiO2 heterojunction composites were tested for photocatalytic reduction of CO2 and it exhibited superior performance and stability. The consequences show that the pure MoS2 demonstrates a poor photocatalytic activity because of its high electron-hole recombination, and the maximum yields of CO and CH4 on 10% MoS2/TiO2 heterojunction composite are 268.97 μmol/g.cat and 49.93μmol/g.cat, respectively, which are about 5.33 times and 16.26 times of pure TiO2 (P25). The improved photocatalytic activity of 10% MoS2/TiO2 heterojunction composite could be put down to the high-efficiency separation of photogenerated electron-hole pairs, strong response to visible light and the narrowed band gap.

Diatomite-Bi2S3 composite photocatalyst: enhanced photocatalytic performance for visible light reduction of Cr(VI)

The Cr(VI) is a acute toxic and bioaccumulated pollutant in wastewater, the removal of these contaminants is particularly significant. Semiconductor photocatalysis is an effective method to reduce the Cr(VI) in the wastewater. In this paper, diatomite/Bi2S3 composite photocatalysts are synthesized by a facile in suit hydrothermal vulcanization method using bismuth nitrate and thiourea as precursors and diatomite as supporting materials. The structural information, morphologies, chemical states and optical properties of the composite are characterized by XRD, SEM, XPS and DRS. Under visible light irradiation (λ > 400 nm), the diatomite/Bi2S3 composite exhibit better photocatalytic reduction activity of Cr(VI) than the pristine Bi2S3. The photocatalytic mechanism is further investigated by the active species capturing tests and photoelectrochemical measurements.

Cu2In2ZnS5/Gd2O2S:Tb for full solar spectrum photoreduction of Cr(VI) and CO2 from UV/vis to near-infrared light

Full solar spectrum active heterogenous photocatalysis for environmental applications remains highly challenging. Here we report the novel Cu2In2ZnS5/Gd2O2S:Tb (CG) hybrid photocatalysts via a facile solvothermal method for efficient Cr(VI) and CO2 reduction. The narrow band gap energies of the CG hybrid photocatalysts synthesized via a facile solvothermal method show excellent absorption and catalytic activity in the full solar spectrum. High Cr(VI) reduction rate of 90% and CH4 production rate of 57.73 μmol h−1 g−1 are achieved for CG hybrid photocatalyst with 1 wt.% Gd2O2S:Tb. The excellent performance is due to the fact that in the hybrid, Gd2O2S:Tb as cocatalyst, provides more active sites and inhibits the recombination of charge carriers due to the synergetic effect between Cu2In2ZnS5 and Gd2O2S:Tb, consequently improving the photocatalytic reduction activity.

A stable 1D mixed-valence CuI/CuII coordination polymer with photocatalytic reduction activity toward Cr(Ⅵ)

A new one-dimensional coordination polymer, [CuII(L)2][CuI(bpy)]2·4H2O (BUC-20) (H2L = cis-1,3-dibenzyl-2-imidazolidone-4,5-dicarboxylic acid, bpy = 4,4-bipyridine), was synthesized solvothermal condition. The crystal structure of BUC-20 was analyzed, and its properties like band energy, water stability, and photocurrent were clarified. BUC-20 exhibited outstanding photocatalytic Cr(VI) performance upon the UV light irradiation under acid condition, which was superior to those of existing photocatalysts. The photocatalytic performance was not influenced by the presence of inorganic ions, which was affirmed by the introduction real surface water to prepare simulated wastewater. BUC-20 exhibited good water stability, and could be used several runs without significant efficiency decrease.