ZnO-based Catalysts Research Articles

Enhancing CO2 photoreduction efficiency with MXene-modified ZnO@Co3O4 double heterojunction

The photocatalytic reduction of CO2 into energy carriers holds significant industrial appeal, but achieving this process kinetically remains challenging due to the lack of well-designed catalysts. This study presents a novel 2D/3D nanostructured photocatalyst, developed by attaching a few-layer Ti3C2 MXene to polyethylenimine (PEI)-modified ZnO@CO3O4 nanocages, which are derived from a bimetallic zinc-cobalt ZIF. The resulting Mx-PEI-ZnO@Co3O4 catalyst achieved impressive yields of CO and CH4 at 594.37 and 42.67 μmol g−1 h−1, respectively, without the need for sacrificial agents and photosensitizers, and maintained remarkable stability across multiple cycles. These yields represent the highest performance for ZnO-based catalysts to date, with quantum efficiency at 380 nm reached up to 25.06 %. The unique S-scheme and Schottky junctions, along with enhanced CO2 adsorption and hydrogen-bond interactions facilitated by the conductive PEI within the Ti3C2/ZnO/Co3O4 double heterojunctions, effectively inhibit electron-hole recombination and significantly enhance CO2 photoreduction performance. This study underscores the combined benefits of double heterojunction engineering, PEI-functionalized CO2 uptake, and MXene co-catalyst integration within a single system, proposing a new approach for designing highly efficient photocatalysts for solar-driven CO2 reduction in energy-efficient fuel production.

A critical mini-review on doping and heterojunction formation in ZnO-based catalysts.

This mini-review on doping and heterojunctions for catalysis applications provides a comprehensive overview of key aspects. Doping, when carried out adequately with a uniform distribution, creates a new energy level that significantly enhances charge transfer and light absorption. This new level alters the material's morphology and enhances intrinsic defects. For instance, ZnO, despite its exceptional band edge concerning oxygen reduction and water oxidation redox potentials, faces the issue of electron-hole recombination. However, forming a heterojunction can effectively aid charge transfer and prolong electron-hole relaxation without recombination. This is where the role of doping and heterojunctions becomes crucial. Additionally, incorporating noble metals with S- and Z-scheme heterojunctions offers a promising mechanism for charge transfer and visible light harvesting, further amplifying the catalytic properties.

Neodymium-Doped Zinc Oxide Nanoparticles Catalytic Cathode for Enhanced Efficiency of Microbial Desalination Cells

The Microbial Desalination Cell is a novel method for desalinating water that also generates energy via substrate oxidation. The MDC comprises three chambers: the anode chamber, the desalination chamber, and the cathode chamber. The fundamental problem with the technology is that it generates very little power during the oxygen reduction reaction (ORR). One solution to this issue is to use a highly active cathode catalyst, which effectively increases the ORR rate. Neodymium-doped ZnO nanoparticles were produced and employed as a cathode catalyst in the three-chambered MDC1 to improve performance. Zn1−xNdxO nanocrystalline samples containing x = 0.0, 0.03, 0.6, and 0.10 were synthesized efficiently through the cost-efficient sol-gel method. Transmission electron microscopy (TEM) and X-ray diffraction techniques revealed the nanocrystalline nature and the phase purity of the Zn1−xNdxO samples. The structural properties of ZnO nanostructured materials were elucidated by Rietveld refinement of the XRD patterns, which showed displacement of Zn and O ions and revealed changes in the electron density around the Zn-O bond with Nd substitution. The local features of light emission from Zn1−xNdxO samples have been studied with photoluminescence. The UV and green-yellow emissions originate from the exciton transition and the transition between the Nd3+ deep level, oxygen vacancy and interstitial oxygen. The results were compared to MDC-2, which did not have a catalyst on the cathode. Both MDCs were tested using a saline water solution containing 15 g/L of NaCl to measure their desalination performance. The better reduction kinetics was confirmed by cyclic voltammetry of the MDC-1 cathode. MDC-1 had a higher desalination efficiency (77.02% ± 2.0%) due to the presence of an Nd-doped ZnO catalyst than MDC-2 (59.3% ± 8.3%). MDC-1’s maximum power density of 3.65 W/m3 was 2.78 times greater than MDC-2’s (0.78 W/m3). Furthermore, the coulombic efficiency of MDC-1 was found to be (8.8 ± 0.3%), which was much higher than that of MDC-2 (4.56 ± 0.2%). As a result, the Nd-doped ZnO-based catalyst developed in this study can potentially improve ORR in MDC cathodes, enabling them to generate more power.

Enhancing photothermal VOCs removal in ZnO-based catalysts via transition metal-based band edge tuning and oxygen vacancy engineering

In this study, the band edge tuning and oxygen vacancy optimization of ZnO-based catalysts were explored via transition metal doping for application to photothermal aromatic and halogenated VOCs degradation. Initial minute doping (0.5 wt %) experiments were conducted to determine the dopant with the highest potential, and it was revealed that Zr4+ doping was able to improve chlorobenzene removal to 74.14 % after 4 h of simulated solar light irradiation at 320 K. Further optimization of Zr (Zr0.05ZnOx; 5 % Zr doping) resulted to even greater reduction of toluene and chlorobenzene, from 300 ppmv to 0.4 ppmv (99.9 %) and 52.9 ppmv (82.4 %), respectively. Additional comparative removal experiments also showed the superior performance of Zr0.05ZnOx in contrast to ZnO. The extent of removal highly depended on the functional group attached, with the removal efficiency following the trend: o-xylene ≥ toluene > benzene > bromobenzene > chlorobenzene. Based from the comprehensive analysis of the EPR, XPS, and UV-DRS results, the observed boost in the photocatalytic activity from pristine ZnO can be attributed to 1) the increase in the concentration of oxygen vacancies, resulting in improving the hole-carrier separation, and 2) the valence band shifts associated to the doping of Zr4+ into the ZnO lattice for an enhanced potential difference towards ·OH generation. Comparison with commercially available photocatalysts (TiO2 and ZnO) also revealed that the VOC removal over sol-gel derived Zr0.05ZnOx was much higher, suggesting immense potential for industrial application.

Electronic Promotion of Methanol Synthesis over Cu-Loaded ZnO-Based Catalysts

Methanol, a raw material for C1 chemistry, is industrially produced under harsh conditions using Cu/ZnO-based catalysts. The synthesis of methanol under mild conditions is a challenging subject using an improved catalyst. Here, Zn1-xSixO (ZSO) nanoparticles were synthesized by a thermal plasma method, and their work function and carrier concentration could be tuned by the Zn:Si ratio. The electrically conductive ZSO nanoparticles with a low work function enhanced the donation of electrons to loaded Cu and significantly promoted hydrogenation of CO to methanol, whereas insulating ZSO nanoparticles with a similar low work function did not. These results reveal that efficient electronic promotion by the transfer of electrons from a support to loaded Cu plays a key role in low-temperature methanol synthesis.

Metallurgical Residue-Derived Cu–ZnO-Based Catalyst for CO2 Hydrogenation to Methanol: An Insight on the Effect of the Preparation Method

Valorization of residual materials in the development of catalytic materials has an appealing potential from the perspective of a sustainable development. For the first time, Fe/Mg-containing metallurgical waste (UGSO) was utilized as a support for the development of innovative catalysts for CO2 hydrogenation into methanol. A series of different CuZn/UGSO catalysts were developed by conventional and modified deposition–coprecipitation methods. The addition of Cu/Zn into the structure of Fe3O4/MgxFeyO4 was found to improve Cu2+ and Zn2+ dispersion, while the presence of MgO favors methanol selectivity. Compared to 10Cu7.5Zn/UGSO (10 wt % Cu, 7.5 wt % Zn), the higher methanol yield obtained over 10Cu7.5Zn/UGSO–EtOH (10 wt % Cu, 7.5 wt % Zn, ethanol addition after coprecipitation) is a result of both higher CO2 conversion [attributed to (i) finer particle sizes of CuO and ZnO, (ii) a higher Cu0/Cu+ percentage, and (iii) higher oxygen vacancies and number of strong basic sites on the catalyst surface] and higher methanol selectivity [assigned to (i) the stronger interaction of Cu and ZnO and (ii) a higher number of medium basic sites] in comparison with its counterpart. This residue-based catalyst offers a 150% higher methanol yield than a commercial Cu-based methanol synthesis catalyst at 260 °C and 20 bar. These promising results can open a window to the utilization of this residue as a catalytic support in other CO2 hydrogenation processes.

Facile synthesis of sunlight driven photocatalysts Zn0.9Ho0.05M0.05O (M = Pr, Sm, Er) for the removal of synthetic dyes from wastewater

Currently, environmental pollution due to contaminants released from industries into clean water is a big challenge to maintain public health worldwide. The elimination of organic toxins, particularly organic dyes using semiconductor-mediated photocatalysis is an efficient technique. Herein, Zn0.9Ho0.05M0.05O (M = Pr, Sm, Er) photocatalysts were prepared by the co-precipitation method and characterized via state-of-art techniques to study the structural, optical, electrochemical, and morphological properties. XRD results confirmed that the grown ZnO-based catalysts have hexagonal wurtzite structures with high crystallinity and successful co-doping. FTIR and Raman analysis have shown the vibrational bands and optical phonon modes of ZnO in all catalysts with a small shift which further evident the co-doping. Roughly spherical morphology revealed by FE-SEM images with improvement by co-doping. The energy bandgap of grown ZnO depends on dopants and is decreased by co-doping compared to single-doped samples, as evident from UV-Visible analysis. The photocatalytic degradation experiment towards methyl orange (MO) and methylene blue (MB) dyes under sunlight exhibited that co-doped catalysts have higher efficiency against both dyes. Remarkably, Ho-Er co-doped catalyst degraded 99.7% MB and 84% MO dye under 60 min sunlight illumination with a higher apparent rate constant of 0.0975 and 0.028 min−1, respectively, with stability up to 6th cycle against MB dye. The scavenger tests demonstrate that the major role in the enhanced photodegradation is superoxide (O2*−) and hydroxyl (OH*) radicals. The boosted photocatalytic activity is due to the lower energy bandgap, and the higher flow of charge carrier (EIS results) led to the higher generation of reactive species. Moreover, these consequences revealed that the individual performance of ZnO could be boosted through rare earth elements co-doping to make it useful for environmental applications.

Engineering the Interfacial Microenvironment via Surface Hydroxylation to Realize the Global Optimization of Electrochemical CO2 Reduction.

The adsorption and activation of CO2 on the electrode interface is a prerequisite and key step for electrocatalytic CO2 reduction reaction (eCO2 RR). Regulating the interfacial microenvironment to promote the adsorption and activation of CO2 is thus of great significance to optimize overall conversion efficiency. Herein, a CO2-philic hydroxyl coordinated ZnO (ZnO–OH) catalyst is fabricated, for the first time, via a facile MOF-assisted method. In comparison to the commercial ZnO, the as-prepared ZnO–OH exhibits much higher selectivity toward CO at lower applied potential, reaching a Faradaic efficiency of 85% at −0.95 V versus RHE. To the best of our knowledge, such selectivity is one of the best records in ZnO-based catalysts reported till date. Density functional theory calculations reveal that the coordinated surficial −OH groups are not only favorable to interact with CO2 molecules but also function in synergy to decrease the energy barrier of the rate-determining step and maintain a higher charge density of potential active sites as well as inhibit undesired hydrogen evolution reaction. Our results indicate that engineering the interfacial microenvironment through the introduction of CO2-philic groups is a promising way to achieve the global optimization of eCO2 RR via promoting adsorption and activation of CO2.

Cellulose template designed porous ZnO based catalysts with different valence copper for solar photocatalytic CO2 conversion

Designing a green method to enhance the utilization of photocatalysts on solar energy was of great significance to alleviate energy problems. The porous ZnO-based catalysts with different valence copper (CuO−ZnOCel-T and Cu−ZnOCel-T) were successfully obtained by using cellulose fibers as templates, which possessed three-dimensional structures and excellent photocatalytic activities. The dispersibility of CuO−ZnOCel-T nanoparticle was influenced by surface groups of cellulose template, the more active sites of composite catalyst were exposed than CuO−ZnO catalysts with carbon fiber as the template and CuO−ZnO powders without any template. Moreover, to explore the effects of different valence states of Cu on the photocatalytic activity of ZnO nanoparticles, wheat straw was used to reduce CuO−ZnOCel-T to Cu−ZnOCel-T by using pyrolysis reduction treatment of wheat straw. The CO production rate of Cu−ZnOCel-T (30.17 µmol*g−1h−1) was significantly higher than CuO−ZnOCel-T (8.61 µmol*g−1h−1) based on the same catalyst morphologies, indicating that the surface plasmon resonance (SPR) effect of Cu was more favorable for improving catalytic activities of ZnO than the structure effect of CuO−ZnOCel-T heterojunction. This work proposed an exciting idea for using biomass materials to tailor the photocatalytic performance of catalysts and reduce copper ions in a cleaner method.

Photodegradation processes of oxcarbazepine under solar simulated radiation: Analysis of transformation products

Oxcarbazepine (OXC) an antiepileptic drug, has been detected in wastewater treatment plant (WWTP) effluents, surface, and groundwater in concentrations ranged from µg L−1 to ng L−1. The presence of this drug and its transformation products (TPs) in the aquatic environment creates uncertainty concerning the potential risks to aquatic species and living beings. In this work, the removal of OXC from the water was conducted by photolysis process and heterogeneous photocatalysis using different ZnO-based catalysts. The TPs formed in both reactions were monitored by LC-MS/MS and UPLC-qTOF-MS. The results showed that the OXC was entirely degraded after 30 min of photolysis and photocatalytic reactions. The formation of the main TPs was similar in both processes: nine TPs were detected in the photolysis, while ten products were identified during the heterogeneous photocatalysis. The photolysis reaction was the main responsible for the formation of TPs in both processes, nevertheless, these TPs remained during the photolysis treatment, while its rapid decomposition was achieved in the photocatalytic process. Different degradation pathways were elucidated based on the detection of the generated products. The main degradation reactions were hydroxylation of OXC, heterocyclic ring photo-oxidation, intramolecular ring closure, and HO• radical attack, which led the destruction of the parent compound oxcarbazepine.

Visible-light driven sonophotocatalytic removal of tetracycline using Ca-doped ZnO nanoparticles

Highly efficient, long-term, eco-friendly catalysts for water decontamination technology are urgently needed to meet the prioritized objectives of green development and societies worldwide. Ca-doped ZnO was investigated as environmentally friendly sono-photocatalytic system under LED visible light irradiation to efficiently mineralize tetracycline-based antibiotics. The effects of pH, Ca doping, light, ultrasound, and pH on the mineralization of tetracycline by Ca-doped ZnO nanopowders and on the chemical, sono-, photo- and sono-photostability of Ca-doped ZnO nanopowders were systematically investigated. The ZnO-based catalyst with 2 at. % of Ca dopant exhibited the best sono-photocatalytic performance in mineralizing tetracyclines under visible LED light and ultrasound irradiation (i.e., ≥99% mineralization in 90 min), with excellent reusability and minimal sono-photocorrosion (i.e., ≤1% of catalyst dissolution in 180 min), which were even greater in the absence of organic pollutants and in the pH range of most natural waters. For Ca-doped ZnO nanopowders, the role of the generated reactive oxygen species under light and ultrasound stimulation and the mechanism of the mineralization of tetracycline were analyzed. In conclusion, the sono-photocatalytic mineralization of antibiotics synergizing visible LED light and weak ultrasound irradiation in the presence of Ca-doped ZnO nanopowders presents an outstanding start to developing highly efficient, long-term, eco-friendly catalysts for efficiently treating emerging organic pollutants.

Boosting photocatalytic activity of g-C3N4/nano-sized ZnO fabricated in CO2-saturated solutions

The g-C3N4/nano-sized ZnO (CZ) composite materials was synthesized as an excellent photocatalyst by a novel route in CO2-saturated solutions. It demonstrates that CZ composite possess high surface areas (63.8 ~ 122.9 m2 g−1) thus can accelerate electron transport and provide more catalytically active sites. The developed CZ-2 composite exhibits outstanding performance with efficiency of 99.9% after 25 min and excellent stability after four recycles. The present route may inspire the development of excellent ZnO-based catalysts and broaden the applications of ZnO.

Atomic structures and electronic properties of Cr-doped ZnO() surfaces

An integrated approach combining scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) is used to investigate the atomic structures and electronic properties of Cr-doped ZnO(▪) surfaces. When deposited at 300 K, Cr at low surface coverage (< 0.1 ML) appeared either as isolated atoms on the surface terrace of ZnO(▪) or substituting Zn atoms in the ZnO lattice. Their structural models could be identified from atomic-resolution STM images and their oxidation states were found as Cr3+ based on XPS measurements. Rectangular islands nucleated at step edges along the [0001] direction could also be observed during the initial growth of Cr at 300 K and were assigned as Cr islands. The density of Cr islands as well as their average size increased with the increasing of Cr surface loading. Thermal treatments at above 600 K could facilitate the decomposition of Cr islands and the re-dispersion of Cr atoms into the ZnO lattice, indicating a strong interaction between Cr and ZnO. The adsorption of CO at 78 K showed no preferential adsorption at Cr3+ sites embedded in the surface lattice of ZnO. However, the re-dispersion of Cr atoms into the ZnO bulk at above 600 K could induce a significant upward band bending, causing a negative shift of core level XPS peaks of Zn 2p and O 1s by ~0.5–0.7 eV. Our study has thus constructed a model catalyst for Cr-doped ZnO and provided atomic insight for understanding ZnO-based catalysts.

Insights into the complementary behaviour of Gd doping in GO/Gd/ZnO composites as an efficient candidate towards photocatalytic degradation of indigo carmine dye

Water pollution caused by the discharge of hazardous organic pollutants from the food, textile, leather and paper industries is becoming a task for sustainable development. Photocatalysis is considered to be an effective method for removing organic contaminants from dye wastewater. The photocatalytic activity of ZnO-based catalyst based on its ability to generate electron–hole pairs upon photoillumination is limited due to its wide bandgap. In this study, novel GO/Gd/ZnO composites with varying percentages (0.3–1%) of Gd were fabricated via a hydrothermal approach and their photocatalytic degradation processes and performance of indigo carmine (IC) dye were investigated under light irradiation. The chemical composition and morphological features of the prepared GO/Gd/ZnO composites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope, energy-dispersive spectroscopy, Brunauer–Emmett–Teller, Raman and Fourier–transform infrared spectroscopy. GO/Gd/ZnO composites show much higher photocatalytic performance with complete IC dye degradation within 30 min of irradiation than bulk ZnO and GO/ZnO composite. Moreover, the optimal performance was revealed by the GO/Gd/ZnO (0.6% Gd) composite (nearly 96% degradation of IC dye). Using density functional theory, we explore the potential drop across the interface, electronic and structural properties of GO/ZnO and GO/Gd/ZnO composites. The photodegradation rate of IC dye by GO/Gd/ZnO (0.6% Gd) composite was 7.65 and 2.94-fold higher than those of bulk ZnO and GO/ZnO composite. The capture experiments revealed ˙O2− and ˙OH as the main active radicals during the photodegradation process. The theoretical and experimental findings obtained in this study indicate that GO/Gd/ZnO photocatalyst has great potential application for eliminating environmental pollutants.

Pressure-dependent band-bending in ZnO: A near-ambient-pressure X-ray photoelectron spectroscopy study

The role of ZnO polar surfaces in the activation of small gas molecules were studied by in-situ NAP-XPS in realistic pressure conditions. ZnO-based catalysts have been intensively studied because of their extraordinary performance in lower olefin synthesis, methanol synthesis and water–gas shift reactions. However, how ZnO catalyzes these reactions are still not well understood. Herein, we investigate the activations of CO 2 , O 2 and CO on single crystalline ZnO polar surfaces at room temperature, through in-situ near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS). It is revealed that O 2 and CO 2 can undergo chemisorption on ZnO polar surfaces at elevated pressures. On the ZnO ( 0001 ) surface, molecular CO 2 (O 2 ) can chemically interact with the top layer Zn atoms, leading to the formation of C O 2 δ - ( O 2 δ - ) or partially dissociative atomic oxygen ( O - ) and hence the electron depletion layer in ZnO. Therefore, an apparent upward band-bending in ZnO ( 0001 ) is observed under the CO 2 and O 2 exposure. On the ZnO ( 000 1 ¯ ) surface, the molecular chemisorbed CO 2 (O 2 ) mainly bond to the surface oxygen vacancies, which also results in an upward band-bending in ZnO ( 000 1 ¯ ). In contrast, no band-bending is observed for both ZnO polar surfaces upon CO exposure. The electron-acceptor nature of the surface bounded molecules/atoms is responsible for the reversible binding energy shift of Zn 2 p 3/2 and O 1 s in ZnO. Our findings can shed light on the fundamental understandings of CO 2 and O 2 activation on ZnO surfaces, especially the role of ZnO in heterogeneous catalytic reactions.

ZnO-Based Catalyst for Photodegradation of 2-Chlorophenol in Aqueous Solution Under Simulated Solar Light Using a Continuous Flow Method

ZnO nanoparticles, stacked on the bottom of a glass dish, were used as a catalyst for the photodegradation of aqueous 2-chlorophenol (2-CP) contaminant. Solutions of 2-CP at different concentrations and pH values were passed over the ZnO film under simulated solar light. The effect of the light intensity on the contaminant photodegradation rate was investigated. The photodegradation efficiency was evaluated based on the percentage degradation, turnover number, turnover frequency, and quantum yield. The reaction efficiency parameters showed no significant variation when changing the pH across moderate values (neutral, slightly basic, and slightly acidic). Complete mineralization of the contaminant to CO2, H2O, and other minerals was confirmed by various analytical methods including high-performance liquid chromatography, ultraviolet–visible (UV–Vis) spectroscopy, and total organic carbon measurements. The continuous flow method applied in this work showed promising results in terms of safe removal of 2-CP from water at laboratory scale. More study of this method is needed to enable its use at larger, pilot plant scale.

Polarity- and Pressure-Dependent Hydrogen Dynamics on ZnO Polar Surfaces Revealed by Near-Ambient-Pressure X-ray Photoelectron Spectroscopy

ZnO-based catalysts have been widely used in industrial reactions involving syngas conversions. Hydrogen dynamics on the surface of the catalyst is an essential process for understanding the mechan...

Room temperature ultrafast synthesis of zinc oxide nanomaterials via hydride generation for non-enzymatic glucose detection

A highly sensitive electrochemical non-enzymatic glucose (Glu) sensor has been developed based on zinc oxide nanomaterials (ZnO NMs), which was synthesized by a novel and ultrafast strategy based on headspace hydride generation (HG) at room temperature (RT). The preparation of ZnO NMs was performed in gas–solid phase by introducing ZnH2 gas (generated on-line by reducing Zn2+ with KBH4) into carbon cloth (CC) in a sealed headspace bottle. ZnH2 was unstable, can easily decompose and react with O2 in the headspace bottle to form ZnO NMs on CC. The whole preparation process was completed in minute-level under ambient conditions, which was utilized to be a feasible catalyst electrode for highly sensitive Glu sensing afterwards. It is found that the developed sensor has an excellent glucose sensing performance with high corresponding sensitivity of 4792 μA mM−1 cm−2, which was better than other ZnO-based catalysts reported. The measurement results indicate that ZnO/CC presents a short response time of less than 3 s, a wide linear range from 1 μM to 1.45 mM, a low detection of limit (LOD) of 0.43 μM (S/N = 3). Besides, the possible mechanism was discussed. Glu in serum samples has been detected with satisfactory results by the proposed material.

Activation and surface reactions of CO and H2 on ZnO powders and nanoplates under CO hydrogenation reaction conditions

Abstract Activation and surface reactions of CO and H2 on ZnO powders and nanoplates under CO hydrogenation reaction conditions were (quasi) in situ studied using temperature programmed surface reaction spectra, diffuse reflectance Fourier transform infrared spectroscopy, inelastic neutron scattering spectroscopy and electron paramagnetic resonance. CO undergoes disproportion reaction to produce gaseous CO2 and surface carbon adatoms, and adsorbs to form surface formate species. H2 adsorption forms dominant irreversibly-adsorbed surface hydroxyl groups and interstitial H species and very minor surface Zn-H species. Surface formate species and hydroxyl groups react to produce CO2 and H2, while surface carbon adatoms are hydrogenated by surface Zn-H species sequentially to produce CH(a), CH2(a), CH3(a) and eventually gaseous CH4. The ZnO nanoplates, exposing a higher fraction of Zn-ZnO(0001) and O-ZnO(000–1) polar facets, are more active than the ZnO powders to catalyze CO hydrogenation to CH4. These results provide fundamental understanding of the reaction mechanisms and structural effects of CO hydrogenation reaction catalyzed by ZnO-based catalysts.

Self-assembled electron-rich interface in defected ZnO:rGO-Cu:Cu2O, and effective visible light-induced carbon dioxide photoreduction

As an ecological mimicry system, carbon dioxide (CO2)-to-fuel conversion in artificial photosynthesis is quite attractive as a method to simultaneously solve the global energy crisis and environmental problems. Although many researchers have spent a lot of time on efficient charge separation and on enhanced light harvesting, photocatalysts still exhibit poor activity. Nevertheless, designing new types of photocatalysts is still worth attempting. Herein, a localized surface plasmon resonance enhanced the self-assembled rGO-Cu electron-rich interface in a defected ZnO:rGO-Cu:Cu2O composite resulted to inhibit the relaxation of excited electrons by continuously supplying electrons into the vacant holes of Cu2O. The defected ZnO exhibited a diminished band-gap and a higher adsorption of CO2. Under visible irradiation, methane (CH4) produced from CO2 accumulated to 41.0 μ mol g−1 over 10 h on def-ZnO:rGO-Cu:Cu2O, which corresponded to at least 10 times the CH4 amounts compared with the reported ZnO-based catalysts. Ultimately, this work provided new approaches for designing photocatalysts to improve CO2 conversion in gas-phase reaction systems as self-assembling the electron-rich interface and inducing the lattice oxygen defect.