Photocatalytic Reduction Activity Research Articles

A novel PVDF film containing g-C3N4@MOF composite for efficient photoreduction of Cr(VI) under visible light

In this study, g-C3N4 was successfully synthesized and combined with MIL-88A to form a composite material (g-C3N4@MIL-88A composite, abbreviated as CNM). With the aid of the phase inversion method, CNM-PVDF composite films were synthesized, integrating various functional components. The CNM Z-scheme heterojunction efficiently harvests visible light, enhances interfacial separation, and suppresses the recombination of photogenerated charge carriers, resulting in significant photoreduction of Cr(VI) (94.01%). However, CNM composites in powder form tend to aggregate without stable support, complicating separation and recycling processes. To address this issue, PVDF is used to immobilize the photocatalyst. The results demonstrate that CNM-PVDF films exhibit superior photocatalytic reduction activity towards Cr(VI), achieving an efficiency of 90.4% under optimal conditions: 20 mg/L of Cr(VI), 3% CNM-PVDF, pH 3, and 180 min of irradiation. This study represents a significant advancement in developing and applying composite films, offering excellent photocatalytic performance. Unlike the powder sample (CNM), the CNM-PVDF composite can be easily recovered for four consecutive cycles, effectively overcoming the challenge of secondary pollution.

Ce4+/Ce3+ redox effect-promoted UiO-66(Ce)/BiOBr heterojunction for enhancement photoreduction CO2 under visible light

Significant differences in the separation efficiency of electrons and holes have the potential to impact the performance of photocatalytic reduction. The objective of this study was to fabricate a BiOBr/UiO-66(Ce) type II heterostructure with the intention of improving the photocatalytic reduction activity. The cycling of Ce4+/Ce3+ within the UiO-66(Ce) structure consumed the electrons and holes, facilitating the separation of photogenerated carriers. BiOBr/UiO-66(Ce) composite demonstrated exceptional visible-light photocatalytic reduction of carbon dioxide. The highest photocatalytic activity was achieved at 2 % mass of UiO-66(Ce), which the carbon monoxide yield was 20.4 µmol·g−1·h−1. The photocatalytic activity of the BiOBr/UiO-66(Ce) composites was 11.08 times higher than BiOBr (1.84 µmol·g−1·h−1). These findings provide new insights into the use of UiO-66(Ce) as a co-catalyst in the photocatalytic reduction of CO.

Efficient Photocatalytic Reduction of Hexavalent Chromium by NiCo2S4/BiOBr Heterogeneous Photocatalysts

For typical Cr(VI)-containing industrial wastewater, more efficient water treatment technologies need to be used to ensure that Cr(VI) concentrations are reduced to safe levels before discharge. Photocatalytic technology is highly efficient, environmentally friendly, and has been extensively used to address this demand. Herein, heterogeneous NiCo2S4/BiOBr photocatalysts with different ratios were prepared using a solvothermal method. When compared with pure NiCo2S4 and BiOBr, the NiCo2S4/BiOBr-30 had significantly increased adsorption capacity and visible-light-driven photocatalytic reduction activity for Cr(VI) removal. The improved adsorption performance of the NiCo2S4/BiOBr-30 was mainly due to its increased specific surface area, and the enhanced photocatalytic performance of the NiCo2S4/BiOBr-30 could be attributed to the improved separation and transfer of photogenerated carriers at the interface. Lastly, a possible enhanced photocatalytic Cr(VI) reduction mechanism of the NiCo2S4/BiOBr heterostructure was developed.

Fabrication of Eu-doped 3D flower-like BiOBr photocatalyst for boosted photoreduction CO2 performance

Here, Eu-doped BiOBr photocatalysts were prepared by a one-step hydrothermal method using ethylene glycol as solvent and hexadecyl trimethyl ammonium bromide (CTAB) as Br source. The photocatalytic CO2 reduction performance of the samples under xenon lamp illumination was examined. The results indicate that Eu doped BiOBr exhibits a higher activity of photocatalytic CO2 reduction to CO/CH4 compared to the reference BiOBr. Moreover, The Eu doped BiOBr sample showed a remarkable stability in cycling experiments. This work provides a useful reference for optimizing design of 3D flower BiOBr photocatalyst to improve photocatalytic CO2 reduction efficiency.

Integration of Cu2O-NiTiO3 as an efficient p-n heterojunction visible light photocatalytic system for the simultaneous removal of Cr (VI) and Alizarine Cyanine Green dye

Cu2O loaded NiTiO3 based p-n heterojunction photocatalysts of various proportions have been synthesized by liquid phase reduction process resulting in NiTiO3 nanoparticles dispersed on the surface of Cu2O. Formation of both oxide phases is confirmed from the XRD, HR-SEM and XPS analysis. Heterojunction formation is confirmed by the intimate contact between NiTiO3 and Cu2O as evidenced by HR-TEM. UV-Vis spectra exhibit a red shift indicating the extended visible light absorption. XPS shows the presence of oxidation states of Ni2+, Ti4+, Cu+, Cu2+ and O2-. Heterojunction materials showed enhanced activity for the simultaneous photocatalytic reduction of Cr (VI) and degradation of Alizarine Cyanine Green dye under visible light irradiation. 1:2 ratio of Cu2O and NiTiO3 heterojunction (1C:2N) material exhibits 100% dye degradation in 90 minutes and Cr (VI) reduction in 180 minutes. Higher activity of Cu2O-NiTiO3 p-n heterojunction is ascribed to the effective charge separation and extended visible light absorption

The Reduced Barrier for the Photogenerated Charge Migration on Covalent Triazine‐Based Frameworks for Boosting Photocatalytic CO2 Reduction Into Syngas

AbstractPhotocatalytic CO2 reduction together with hydrogen generation is a promising approach to generate syngas, the photogenerated electron migration from photosensitizers to the catalytic active sites is the rate‐determining step. Herein, an integrative strategy is presented by covalently grafting metal complexes into donor–acceptor covalent triazine‐based frameworks. The catalytic active sites are integrated with the photosensitizer units by covalent linkages to form an extended π‐conjugated framework, which significantly reduces the energy barrier for the migration of the photogenerated charge carriers, resulting in high activity and durability in photocatalytic CO2 reduction into syngas under visible light irradiation. The CO and H2 evolution amounts in 1.5 h are 1086 and 1042 µmol g−1, respectively, which greatly surpass those in the host‐guest counterparts. Furthermore, selective adsorption for CO2 over N2 renders this photocatalytic system to be effective for syngas production from the simulated flue gas. This study provides new approaches to construct the integrative photocatalytic systems for solar‐to‐chemical energy conversion.

Incorporating ReS2 Nanosheet into ZnIn2S4 Nanoflower as Synergistic Z-Scheme Photocatalyst for Highly Effective and Stable Visible-Light-Driven Photocatalytic Hydrogen Evolution and Degradation.

Inspired by natural photosynthesis, the visible-light-driven Z-scheme system is very effective and promising for boosting photocatalytic hydrogen production and pollutant degradation. Here, a synergistic Z-scheme photocatalyst is constructed by coupling ReS2 nanosheet and ZnIn2S4 nanoflower and the experimental evidence for this direct Z-scheme heterostructure is provided by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and electron paramagnetic resonance. Consequently, such a unique nanostructure makes this Z-scheme heterostructure exhibit 23.7 times higher photocatalytic hydrogen production than that of ZnIn2S4 nanoflower. Moreover, the ZnIn2S4/ReS2 photocatalyst is also very stable for photocatalytic hydrogen evolution, almost without activity decay even storing for two weeks. Besides, this Z-scheme heterostructure also exhibits superior photocatalytic degradation rates of methylene blue (1.7 × 10-2 min-1) and mitoxantrone (4.2 × 10-3 min-1) than that of ZnIn2S4 photocatalyst. The ultraviolet-visible absorption spectra, transient photocurrent spectra, open-circuit potential measurement, and electrochemical impedance spectroscopy reveal that the superior photocatalytic performance of ZnIn2S4/ReS2 heterostructure is mostly attributed to its broad and strong visible-light absorption, effective separation of charge carrier, and improved redox ability. This work provides a promising nanostructure design of a visible-light-driven Z-scheme heterostructure to simultaneously promote photocatalytic reduction and oxidation activity.

Fabrication of CdIn2S4/ZnS S-scheme heterojunction via in-situ phase transformation for boosting photocatalytic conversion of organic compounds

Developing efficient photocatalysts is one of green and low cost tactic for addressing the environmental deterioration and energy crisis. Therefore, it remains a fantastic and important strategy to design an efficient junction between different semiconductors for harvesting solar light, boosting the redox capability. Herein, the fabrication of ZnS in situ decorated CdIn2S4 (referred to as CIS-Zx) were prepared by converting ZnS particles on Cd2In4S surface by a facile cation exchange method during solvothermal synthesis. According to a series of PEC measurements and DFT calculations, the bending of band edge as well as the establishing of built-in electric field in the interface of CIS/ZnS heterojunction were concluded, causing the formation of in-situ S-scheme heterojunctions in CdIn2S4/ZnS. The in-situ S-scheme heterojunctions can effectively ameliorate the migration behaviors of photo-generated charges. Compared with pure CdInS4, ZnS and physically mixed CdIn2S4/ZnS, the CIS-Zxin-situ S-scheme heterojunction exhibits efficient photocatalytic activity and stability in the selective reduction of aromatic nitro compounds and oxidation of aromatic alcohols, it is hoped that this work will open up a new avenue for innovative applications of in-situ S-scheme heterojunctions.

Adsorption Performance and Photocatalytic Activity of La-TiO2@kaolin Composites

Abstract La-TiO2@kaolin(LTK) composites were prepared via sol-gel method with kaolin, lanthanum nitrate and tetrabutyl titanate as raw materials. The samples were characterized by XRD, SEM/EDS, and UV-Vis. The visible light photocatalytic reduction activity and adsorption performance of samples for Cr(VI) were studied. The results showed that La doping can refine TiO2 grains, stabilize phase structure of anatase TiO2, and expand its absorption spectrum, thereby enhancing its photocatalytic reduction activity. Due to the composite of kaolin, the dispersion of TiO2 is improves and it is endowed with a large specific surface area lead to enhance its adsorption ability for Cr(VI). The adsorption equilibrium process of LTK for Cr(VI) conforms to the Langmuir equation model. The coupling effect of doping and composite modification improves the adsorption and visible light catalytic reduction activity of Cr(VI) over composite material samples. The adsorption-photocatalytic removal rate of LTK for Cr(VI) under visible light irradiation for 6 hours reached the highest of 96.5%. The apparent first-order kinetic constant of its photocatalytic reduction reaction was 2.6 times that of pure TiO2.

0D/2D S-scheme heterojunction of cadmium selenide and covalent triazine frameworks with enhanced photocatalytic activity for hydrogen evolution, carbon dioxide reduction and terpene dehydrogenation

The step-scheme (S-scheme) heterojunction shows the merits of controlling the directional transfer of photogenerated charge carriers and realizing a strong redox potential for photocatalytic hydrogen evolution and carbon dioxide reduction. In this paper, a zero/two-dimensional (0D/2D) S-scheme heterojunction composed of cadmium selenide quantum dots and covalent triazine frameworks (CdSe/CTF) is designed and fabricated by an electrostatic self-assembly approach. Compared with pristine CTF and CdSe quantum dots, the photocatalytic activities of CdSe/CTF composites for hydrogen evolution, carbon dioxide reduction and terpene oxidation are significantly enhanced. The hydrogen evolution rate of CdSe/CTF hybrid photocatalyst immobilized with platinum nanoparticles as cocatalyst reached 19.0 mmol g−1 h−1 under visible-light irradiation, and the apparent quantum yield is 9.8 % at 420 nm. The CdSe/CTF hybrid also exhibited more superior photocatalytic activity in carbon dioxide reduction with a carbon monoxide evolution rate of 1.48 mmol g−1 h−1, and presented higher photocatalytic reactivity in the selective oxidation of α-terpinene to p-cymene. The remarkable enhancement of photocatalytic performance for CdSe/CTF composite is mainly attributed to the facilitated separation and transfer of photoexcited charge carriers of 0D/2D S-scheme heterojunction. This work provides an in-depth insight of utilizing semiconducting polymers as a suitable platform to sustainably transform inexhaustive solar energy to storable chemical energy.

Green synthesis of TiO2 nanoparticles using Echinops echinatus plant extract and its potential applications for photocatalytic dye degradation, 4-nitrophenol reduction, and antimicrobial activity

Green synthesis of TiO2 nanoparticles using Echinops echinatus plant extract and its potential applications for photocatalytic dye degradation, 4-nitrophenol reduction, and antimicrobial activity

One-pot construction of α-Fe2O3/ZnNiFe2O4 heterojunction by incomplete sol/gel-self-propagating method with choline chloride-ethylene glycol media and its photo-degradation performance

A magnetic α-Fe2O3/ZnNiFe2O4 composite photocatalyst was synthesized through a one-pot reaction employing choline chloride-ethylene glycol deep eutectic solvents and an incomplete sol-gel self-propagating method. The photocatalytic performance was assessed by removing methylene blue (MB) under 40 W visible light. With a 1.0 g/L catalyst dosage, 10 mg/L MB concentration, and pH levels of 6 and 12, removal rates of 97 % and 99 % were achieved within 90 min, respectively. The composite also demonstrated effective degradation of methyl orange (MO) and malachite green (MG). Stability tests revealed minimal reduction in photocatalytic activity after four cycles. Active species analysis identified ·O2⁻ and ·OH as the primary agents in the photocatalytic process. XRD, XPS, UV–VIS DRS, HRTEM, PL, and EIS analyses confirmed the formation of a Z-scheme heterojunction between ZnNiFe2O4 and α-Fe2O3, which enhanced the specific surface area, electron transport capacity, and narrowed the band gap. This heterojunction improved the separation efficiency of photogenerated electron-hole pairs, resulting in enhanced photocatalytic activity and stability. This study presents a novel approach for preparing Z-scheme heterojunction photocatalysts through a one-pot reaction.

An Ester-Functionalized Bidentate Titanium-based Metal-Organic Framework with Visible-Light Enhanced Activity for CO2 Photoreduction.

The limited visible light response is a critical drawback that hampers the photocatalytic efficacy of Ti-MOFs. However, study concerning the enhancement of the visible-light response of Ti-MOFs is still in its nascent stage. In this study, we employ the 'dual-ligand decrystallization strategy' to manipulate the electronic environment of Ti4+, leading to the synthesis of three ester-functionalized bidentate Ti-MOFs with enhanced visible light response. Our findings reveal that this approach not only reduces the bandgap of Ti-MOFs but also enhances their photocatalytic activity for carbon dioxide reduction. Specifically, compared to the bandgap of Ti-BPDC at 2.98 eV, the bandgap of Ti-BPDC-CA 1 : 2 has been reduced to 2.14 eV. Moreover, Ti-BPDC-CA 1 : 2 exhibits extraordinary photocatalytic activity with the formic acid (HCOOH) production rate of 617 μmol g-1 h-1 with over 99.5 % selectivity, which is 3.47 times higher than that of Ti-BPDC. Besides providing a cost-effective strategy for enhancing the visible light response of Ti-MOFs, our study also serves as an illustrative example for establishing the correlation between electronic structure and optical properties.

One step synthesis of novel Cu3N/Cu2O/C3N4/Cu composite and their photocatalytic reduction activities

Copper nitride/cuprous oxide/carbon nitride/copper (Cu3N/Cu2O/C3N4/Cu) composite material was synthesized by one step thermal decomposition of copper-melamine complexes under N2 atmosphere. The as-synthesized powders were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS). The XRD analysis showed the mix phase of Cu3N, Cu2O, C3N4 and Cu. The photocatalytic activities of Cu3N/Cu2O/C3N4/Cu composite photocatalysts were evaluated by testing the photoreduction of chromium (VI) under UV–visible light irradiation. The results indicated that the synthesized samples are attractive photocatalysts for reduction of chromium (VI) under UV light irradiation. The photoreduction efficiencies of Cu3N/Cu2O/C3N4/Cu composite at 550 °C with TEOA induced by UV light within 120 min were 92.03 % caused by charge diffusion at the Cu3N/Cu2O/C3N4/Cu interface. The results indicated that the synthesized samples are attractive photocatalysts for reduction of chromium (VI) under UV light irradiation.

Halogen-functionalized covalent organic frameworks for photocatalytic Cr(VI) reduction under visible light

Covalent organic frameworks (COFs) are a type of novel organic catalysts which show great potential in the treatment of environmental contaminations. Herein, we synthesized three isoreticular halogen-functionalized (F, Cl and Br) porphyrin COFs for visible-light (420 nm ≤ λ ≤ 780 nm) photocatalytic reduction of Cr(VI) to Cr(III). Halogen substituents with tunable electronegativity can regulate the band structure and modulate the charge carrier kinetics of COFs. In the absence of any sacrificial reagent, the isoreticular COFs exhibited good photocatalytic reduction activity of Cr(VI). Particularly, the TAPP-2F showed nearly 100 % conversion efficiency and the highest reaction rate constants (k) on account of the strong electronegativity of F substituent. Experimental results and theoretical calculations showed that the conduction band (CB) potentials of COFs became more negative and charge carrier separation increased with the enhancement of electronegativity (Br < Cl < F), which could provide sufficient driving force for the photoreduction of Cr(VI) to Cr(III). The halogen substituents strategy for regulating the electronic structure of COFs can provide opportunities for designing efficient photocatalysts for environmental remediation. Meanwhile, the mechanistic insights reported in this study help to understand the photocatalytic degradation pathways of heavy metals.

Penternary Wurtzitic Nitrides Li1-xZnxGe2-xGaxN3: Powder Synthesis, Crystal Structure, and Potentiality as a Solar-Active Photocatalyst.

We developed a new penternary wurtzitic nitride system Li1-xZnxGe2-xGaxN3 (0 ≤ x ≤ 1) by hybridizing LiGe2N3 and ZnGeGaN3. Fairly stoichiometric fine powder samples were synthesized by the reduction-nitridation process at 900 °C. While the end member LiGe2N3 possessed a relatively large band gap of 4.16 eV, the band gap of the developed penternary system varied in a broad range of 3.81 to 3.10 eV, showing promising responsivity to the solar spectrum. The crystal structure of LiGe2N3 was precisely determined by time-of-flight neutron powder diffraction for the first time, revealing the complete ordering of Li and Ge in the Cmc21 structure. The structural evolution from completely ordered LiGe2N3 to fully disordered ZnGeGaN3 was quantitatively analyzed by Rietveld refinement based on a partially disordered Cmc21 model, and the obtained results were also supported by 71Ga solid-state NMR spectroscopy. The synthesized Li1-xZnxGe2-xGaxN3 powder samples exhibited photocatalytic activities for the water reduction and oxidation reactions under solar light irradiation, with the H2 evolution rate of 0.3-59.0 μmol/h and the O2 evolution rate of 3.1-296.2 μmol/h, depending on the composition. Stable solar hydrogen generation of up to 48 h was demonstrated by the x = 0.80 sample, with the total amount of H2 evolved over 1.6 mmol and an external quantum efficiency of 2.1%.

Synergistic Engineering of Energy Band Alignment and Interfacial Electric Field Distribution over Bi-bismuth-Based Hetero-nanofibers for Boosting Visible-Light-Driven Photocatalytic Ammonia Synthesis and Antibiotic Removal.

Synergistic engineering of energy band alignment and interfacial electric field distribution is essential for photocatalyst design but is still challenging because of the limitation on refined regulation in the nanoscale. This study addresses the issue by employing surface modification and thermal-induced phase transformation in Bi2MoO6/BixOyIz hetero-nanofiber frameworks. The energy band alignment switches from a type-II interface to a Z-scheme contact with stronger redox potentials and inhibited electron traps, and the optimized built-in electric field distribution could be reached based on experimental and theoretical investigations. The engineered hetero-nanofibers exhibit outstanding visible-light-driven photocatalytic nitrogen reduction activity (605 μmol/g/h) and tetracycline hydrochloride removal rate (81.5% within 30 min), ranking them among the top-performing bismuth series materials. Furthermore, the photocatalysts show promise in activating advanced oxidants for efficient organic pollutant degradation. Moreover, the Bi2MoO6/Bi5O7I hetero-nanofibers possess good recycling stability owing to their three-dimensional network structure. This research offers valuable insights into heterojunction design for environmental remediation and industrial applications.

Insights into the effect of Ni doping on In2S3 for enhanced activity and selectivity of photocatalytic CO2 reduction

The limited photocatalytic CO2 reduction performance mainly lies in the low utilization of photogenerated electrons during the reaction. In this work, we developed the defect level within the Ni-doped In2S3 nanotube photocatalysts via a simple solvothermal method to increase the available amount of photogenerated electrons for enhanced photocatalytic CO2 reduction performance than the pristine In2S3. The introduction of Ni element into the lattice of In2S3 could significantly improve the photocatalytic activity and selectivity without destruction of the nanotube structure of In2S3. The yield of CO reaches 243.2 μmol/g/h under visible light, which is the highest reported value among In2S3 photocatalysts, and is 8.2 times more than the pure In2S3. Moreover, by modulating the doping amount of Ni element, the selectivity of CO varied from 27.7% to 51.0%. Further characterizations suggest that the doping of Ni element altered the electronic bandgap arrangement of In2S3, where the position of the conduction band is conducive to the activation of CO2 molecules. Moreover, the defect level resulting from Ni-doping not only facilitates the separation of photoexcited electron-hole pairs but also suppresses the recombination of electrons and holes. This study provides an available and reliable strategy for enhancing the photocatalytic CO2 reduction performance of related sulfide photocatalytic materials in future studies.

Na-mediated carbon nitride realizing CO2 photoreduction with selectivity modulation

The depressed directional separation of photogenerated carriers and weak CO2 adsorption/activation activity are the main factors hampering the development of artificial photosynthesis. Herein, Na ions are embedded in graphitic carbon nitride (g-C3N4) to achieve directional migration of the photogenerated electrons to Na sites, while the electron-rich Na sites enhance CO2 adsorption and activation. Na/g-C3N4 (NaCN) shows improved photocatalytic reduction activity of CO2 to CO and CH4, and under simulated sunlight irradiation, the CO yield of NaCN synthesized by embedding Na at 550°C (NaCN-550) is 371.2 μmol g−1 h−1, which is 58.9 times more than that of the monomer g-C3N4. By means of theoretical calculations and experiments including in situ fourier transform infrared spectroscopy, the mechanism is investigated. This strategy which improves carrier separation and reduces the energy barrier at the same time is important to the development of artificial photosynthesis.

The construction of Cs3MoxSbyBr9/BiVO4 S-scheme heterojunction photocatalyst for efficient photocatalytic N2 fixation

Synergistic nitrogen (N2) reduction with water (H2O) oxidation is meaningful but challenging owing to the inertness of the N2 molecule and the sluggish kinetics of H2O oxidation. Herein, a simutaneous-promotion strategy of redox capacities is presented for constructing a lead-free Cs3Sb2Br9-based S-scheme heterojunction, by decorating Mo-functionalized Cs3Sb2Br9 nanocrystals (Cs3MoxSbyBr9) on BiVO4 nanosheet through an in-situ plane-to-point growth manner. The Mo-functionalization for Cs3Sb2Br9 enables the regulation of the d-band center position, greatly improving surface reaction kinetics for N2 reduction. Furthermore, the construction of the S-scheme heterojunction enhances the driving force for H2O oxidation and spatial charge separation of photocatalysts. As anticipated, the resultant Cs3MoxSbyBr9/BiVO4 exhibits an excellent photocatalytic N2 reduction activity under ambient atmosphere, achieving ammonia (NH3) production at a rate of 300 ± 5 μmol g−1 h−1 under simulated sunlight illumination (100 mW cm−2), which is nearly 20-fold higher than that of pristine Cs3Sb2Br9.