Photocatalytic Reduction Activity Research Articles

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.

Facile synthesis, microstructure, photo-catalytic activity, and anti-bacterial property of the novel Ag@gelatin–silica hybrid nanofiber membranes

In this study, novel fibrous membranes made of Ag@gelatin–silica hybrid nanofibers were synthesized from gelatin, 3-glycidoxypropyl trimethoxysilane, and Ag@gelatin nanoparticles (NPs) via a combined method of in situ reduction, sol–gel route, and electrospinning method. Their microstructure, photo-catalytic activity, and anti-bacterial property were evaluated. SEM and TEM observations showed that they were constructed by numerous Ag@gelatin–silica hybrid nanofibers whose surfaces were rough and constructed by numerous Ag@gelatin NPs with the diameter of 10–30 nm. XRD patterns showed that they presented some typical diffractive peak at 39°, 45°, 65°, and 78°, all of which were assigned to Ag NPs. After incubation with the solution of 4-NP and NaBH4, they presented strong photo-catalytic activity for reduction of 4-nitrophenol to 4-aminophenol and their photo-catalytic activity could be well adjusted through adjustment of the content of Ag in the Ag@gelatin–silica hybrid nanofibers. Moreover, they could be easily recycled with a high recovery efficiency. In addition, when exposed to Escherichia coli (E. coli), they showed strong anti-bacterial property and highly inhibited the growth of E. coli. These results indicated that the present hybrid nanofiber membranes are applicable to the multi-functional materials for removal of both organic pollutants and microbial contaminants in the wastewater.

Fabrication of the Heterojunction Photocatalyst MoS2/BiOI and Its Investigation of Its Photocatalytic Reduction and Oxidation Activities

Based on a two-step approach, a flower-like MoS2/BiOI composite with a heterojunction has been successfully fabricated. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared MoS2/BiOI. The formation mechanism of this heterostructure was investigated. The valence band (VB) and conduction band (CB) of the MoS2/BiOI heterojunction have been calculated based on electrochemical characterization, implying the formation of a type I band alignment. The photodegradation of Rhodamine B (RhB) and Cr6+ were used to assess photocatalytic reduction and oxidation activities. The results show that the MoS2/BiOI composite structures perform much better than pristine MoS2 and BiOI. Among the composites with various MoS2 contents, 2% MoS2/BiOI exhibits the best efficiency with respect to the degradation of RhB. After irradiation for 20 minutes, the degradation rate of RhB was 98.82%, which is 1.79 times higher than that using pure BiOI. After irradiation for 80 minutes, the removal of Cr6+ was 97.87%, which is 3.85 times higher than that using pure BiOI. Holes and·O2- are the main reactive species during the photocatalytic process of RhB degradation; holes play the leading role.

Synergistic Effect Between WO3/Activated Carbon and BiVO4 Nanoparticles for Improved Photocatalytic Hydrogen Evolution

Modified composite of the pure monoclinic tungstun oxide with 2.0% of activated carbon photocatalyst with BiVO4 as coupling content is synthezed via facile hydrothermal route. The composite is fabricated with coupling ratio of 0.5%,1.0%,1.5% and 2.0% dopant BiVO4. These composite were characterized by the XRD, SEM, UV–Vis, PL and BET to investigate the various properties (particle size, structural, morphological, purity and optical) and the energy band of the photocatalytic material. It is commonly examined that the C-WO3 showed the extraneous results for the evolution of the hydrogen energy by increasing the coupling contents upto 1.5% of BiVO4 and gave extraordinary photocatalytic activity towards the hydrogen energy production. The formation of the orthorhombic phases from the monoclinic and hexagonal at 2.0% of doping content indicated the increase of size of the particles and energy band gap. The average grain size of the composite is ranging from 30 to 50 nm. The increment of the BiVO4 content in the C-WO3 composite causes the reduction of photocatalytic activity because of the increase in the grain size and the forbidden gap of the photocatalytic composite.

Efficient photocatalytic nitrogen fixation under ambient conditions enabled by the heterojunctions of n-type Bi2MoO6 and oxygen-vacancy-rich p-type BiOBr.

N2 fixation is one of the most important chemical reactions in the ecosystem of our planet. However, the industrial Haber-Bosch ammonia synthesis process is restricted by harsh reaction conditions (350-550 °C, 150-350 atm) and undesirable environmental effects (a large amount of CO2 emission). Photocatalytic N2 fixation is promising for achieving sustainable ammonia synthesis under ambient conditions with lower energy input and less environmental issues. However, the known photocatalysts for N2 reduction under mild conditions still face the great challenge of very low energy conversion efficiency. Herein, we report a facile solution-phase method to prepare the heterojunctions based on n-type Bi2MoO6 nanorods and oxygen-vacancy-rich p-type BiOBr nanosheets (Bi2MoO6/OV-BiOBr). Originating from the formation of p-n junctions and suitable bandgap configuration, the Bi2MoO6/OV-BiOBr heterojunctions exhibit effective light utilization and photogenerated electron-hole separation properties. Moreover, it is confirmed that the oxygen vacancies on BiOBr nanosheets are propitious to the adsorption and activation of N2 molecules. Benefiting from these merits, the Bi2MoO6/OV-BiOBr heterojunctions exhibit improved photocatalytic performance for N2 conversion to ammonia without any noble metal co-catalysts and sacrificial reagents under ambient conditions.

A molecular noble metal-free system for efficient visible light-driven reduction of CO2 to CO.

A new pentadentate quinoline-pyridine ligand and its iron (1), cobalt (2) and nickel (3) complexes have been synthesized and characterized. The iron complex exhibits excellent photocatalytic activity towards CO2-to-CO conversion with a TON(CO) of 544 and a selectivity of 99.3% using the commercially available organic dye purpurin as the photosensitiser and BIH as the electron donor. In contrast, the cobalt and nickel complexes result in very low activity for CO production with a TON of only 8 and 15, respectively. On the other hand, all the three complexes show good electrocatalytic activity for CO2 reduction when using 2,2,2-trifluoroethanol as the proton source with the active intermediate of M0 species. The lack of activity in photocatalytic CO2 reduction by 2 and 3 can be attributed to the redox potential of MI/M0 which is significantly more negative than that of PP-/PP2- while in the case of 1 the FeI/Fe0 redox potential becomes more positive than that of the PP-/PP2- couple.

Engineering a CsPbBr3-based nanocomposite for efficient photocatalytic CO2 reduction: improved charge separation concomitant with increased activity sites.

Metal-halide perovskite nanocrystals have emerged as one of the promising photocatalysts in the photocatalysis field owing to their low-cost and excellent optoelectronic properties. However, this type of nanocrystals generally displays low activity in photocatalytic CO2 reduction owing to the lack of intrinsic catalytic sites and insufficient charge separation. Herein, we functionalized CsPbBr3 nanocrystals with graphitic carbon nitride, containing titanium-oxide species (TiO-CN) to develop an efficient composite catalyst system for photocatalytic CO2 reduction using water as the electron source. Compared to its congener with pristine CsPbBr3, the introduction of TiO-CN could not only increase the number of active sites, but also led to a swift interfacial charge separation between CsPbBr3 and TiO-CN due to their favorable energy-offsets and strong chemical bonding behaviors, which endowed this composite system with an obviously enhanced photocatalytic activity in the reduction of CO2 to CO with water as the sacrificial reductant. Over 3-fold and 6-fold higher activities than those of pristine CsPbBr3 nanocrystals and TiO-CN nanosheets, respectively, were observed under visible light irradiation. Our study provides an effective strategy for improving the photocatalytic activity of metal-halide perovskite nanocrystals, thus promoting their photocatalytic application in the field of artificial photosynthesis.