Tunable Photocatalytic Activity Research Articles

Regulation of Lewis acid sites on ZnO/SiW11Co for tunable photocatalytic activity toward water remediation

The function of surface acidity in catalytic reactions has been well studied in the field of conventional catalysis, nevertheless, regulating surface acidic sites and unveiling its roles during heterogeneous photocatalysis has been less frequently reported. To address this issue, we constructed a novel heterojunction photocatalyst of ZnO/SiW11Co with abundant Lewis acid sites for wastewater treatment. Under visible light irradiation, the optimal ZnO/SiW11Co was found to have the highest photocatalytic activity, achieving a degradation efficiency of 97.7% for Rhodamine B (RhB), 96.1% for tetracycline (TC), and 91.4% for methyl orange (MO). The RhB removal rate remained at 91.3% even after five cycles, indicating excellent stability and practicality of ZnO/SiW11Co. By compositing with SiW11Co, a typical polyoxometalates with unique super acid properties, ZnO/SiW11Co formed plentiful surface Lewis acid sites, as confirmed by the pyridine adsorption FT-IR and NH3-TPD. The as-formed Lewis acid sites could provide more active sites, making it easier for reactants to coordinate to the photocatalyst surface, which reduced the activation energy of photocatalytic reactions and accelerate RhB removal. Density functional theory (DFT) calculations unveiled the redistribution of electron-hole pairs, optimizing the light absorption and charge separation efficiency, which obeyed a Z-scheme mechanism. Combined active species capture experiments and electron spin resonance, •O2−, h+, and •OH were the main active substances for the photocatalytic degradation of RhB. Besides, the possible degradation pathways for RhB were analyzed using liquid chromatography-mass spectrometry (LC-MS). The work provided useful strategy for the design of high-performance photocatalysts via regulating surface Lewis acid sites toward water remediation.

Versatile MOF-based nanofibrous heterostructures for engineering the CO2 photoreduction activity and selectivity: From CO to C2H5OH

Photocatalytic CO2 reduction is a potential promising strategy for eliminating the global energy crisis and environmental issue. However, the complex reduction pathway leads to multiple possible products with limited efficiency, representing a great barrier for the further development. Herein, we report a Metal-organic framework (MOF) based heterostructure model for the efficient photoreduction of CO2 with full controllable product selectivity between CO and C2H5OH. Novel core-sheath like MOF@TiO2 heterostructures could be efficiently prepared by the layer-by-layer (LBL) growth of HKUST-1 onto Cu-embedded TiO2 nanofibers (NFs), affording covalent heterointerfaces for efficient S-scheme charge separation and promising potential in photocatalytic activity regulation. By improving the CO2 capture and retention via in situ amino-functionalization of HKUST-1, the photocatalytic CO production rate could be greatly promoted from 8.76 ± 0.84 to 43.46 ± 0.86 μmol g−1h−1 accompanied by an enhancement of selectivity from 91.7 % to 98.3 %. Moreover, the product could be efficiently engineered into ethanol with a C2 product selectivity of 94.2 % by introducing Cu nanoparticles (NPs) as the additional CC coupling site. The in situ FT-IR and DFT calculations reveal the mechanistic process and decisive role of amino-functionalization and Cu NPs deposition in photocatalytic activity engineering. This work highlights the key factors and significance of fabricating MOFs based heterostructures with tunable photocatalytic activity for achieving CO2 neutralization.

Construction of core-shell cesium lead bromide-silica by precipitation coating method with applications in aqueous photocatalysis

All-inorganic perovskite cesium lead bromide (CsPbBr3) is hardly applied in direct aqueous photocatalysis due to its instability in water although it has received considerable attention in solar energy conversion. Herein, core-shell cesium lead bromide-silica (CsPbBr3@SiO2) has been prepared by a simple precipitation coating method and applied in visible-light-induced photodegradation of antibiotic residue in water for the first time. The obtained CsPbBr3@SiO2 composite exhibits tunable photocatalytic activity according to the precursor ratios and the maximum achieves at lead bromide/tetramethoxysilane (PbBr2/TMOS) molar ratio of 1:5. Electrochemical and photoluminescence analyses indicate that the introduction of SiO2 results in promoted photo-generated current and reduced impedance, which reduces the photo-induced electron-hole recombination and/or the energy barrier of the interfacial reaction between the formed perovskite particulates. Holes (h+) and superoxide radicals (O2−) are identified as active substances for photodegradation activity. This work demonstrates the application of all-inorganic halide perovskite in efficiently treating refractory contaminants in water, which provides an alternative approach for utilizing inorganic perovskites and new ideas for developing high-efficiency photocatalysts.

Stable 3D neutral gallium thioantimonate frameworks decorated with transition metal complexes for a tunable photocatalytic hydrogen evolution

Three novel stable isostructural 3D neutral gallium thioantimonate frameworks decorated with transition metal complexes, exhibiting tunable photocatalytic H2 activity, were synthesized.

Highly Ordered Inverse Opal Structures Synthesized from Shape-Controlled Nanocrystal Building Blocks.

Three-dimensional ordered porous materials known as inverse opal films (IOFs) were synthesized using nanocrystals with precisely defined morphologies. Comprehensive theoretical and experimental studies of the volume fraction ratio and electrostatic interactions between nanocrystals and polystyrene templating particles enabled the formation of highly ordered crack-free photonic structures. The synthetic strategy was first demonstrated using titanium dioxide (TiO2 ) nanocrystals of different shapes and then generalized to assemble nanocrystals of other functional materials, such as indium tin oxide and zinc-doped ferrite. Tunable photocatalytic activity of the TiO2 IOFs, modulated through the choice of the shape of TiO2 nanocrystals in conjunction with selecting desired macroscopic features of the IOF, was further explored. In particular, enhanced activity is observed for crack-free, highly ordered IOFs whose photonic properties can improve light absorption via the slow light effect. This study opens new opportunities in designing multi-length-scale porous nanoarchitectures having enhanced performance in a variety of applications.

Highly Ordered Inverse Opal Structures Synthesized from Shape‐Controlled Nanocrystal Building Blocks

AbstractThree‐dimensional ordered porous materials known as inverse opal films (IOFs) were synthesized using nanocrystals with precisely defined morphologies. Comprehensive theoretical and experimental studies of the volume fraction ratio and electrostatic interactions between nanocrystals and polystyrene templating particles enabled the formation of highly ordered crack‐free photonic structures. The synthetic strategy was first demonstrated using titanium dioxide (TiO2) nanocrystals of different shapes and then generalized to assemble nanocrystals of other functional materials, such as indium tin oxide and zinc‐doped ferrite. Tunable photocatalytic activity of the TiO2 IOFs, modulated through the choice of the shape of TiO2 nanocrystals in conjunction with selecting desired macroscopic features of the IOF, was further explored. In particular, enhanced activity is observed for crack‐free, highly ordered IOFs whose photonic properties can improve light absorption via the slow light effect. This study opens new opportunities in designing multi‐length‐scale porous nanoarchitectures having enhanced performance in a variety of applications.

Tunable Photocatalytic Activity of PEO‐Stabilized ZnO–Polyoxometalate Nanostructures in Aqueous Solution

AbstractThe photocatalytic activity and selectivity of novel binary and ternary composite nanostructures from polyethylene oxide‐stabilized zinc oxide (PEO–ZnO) with and without polyoxometalate (H4[Si(W3O10)4], POM) are determined in aqueous solution under UV‐light. Mono‐ and di‐COOH‐end‐functionalized PEO polymers are used as surface modifiers, influencing the morphology and stability of the ZnO nanoparticles being synthesized in water. POM acts as an additional versatile photocatalytically active building block resulting in a ternary hybrid structure with tunable photocatalytic activity. Catalytic selectivity is demonstrated by studying photocatalytic dye degradations as model reactions, where the chemical backbone of the dyes and their charge turn out to be the basis for the selectivity. All samples are characterized with dynamic light scattering, transmission electron microscopy, scanning electron microscopy, light microscopy, and ζ‐potential measurements. With the functionalized PEOs, large ZnO clusters consisting of leaves are formed while 2‐[2‐(2‐methoxyethoxy) ethoxy] acetic acid (TODA) yields ZnO flower‐like structures.

Cu-Deficient plasmonic Cu2−xS nanocrystals induced tunable photocatalytic activities

Cu-Deficient plasmonic Cu2−xS nanocrystals with tunable photocatalytic activities were synthesized and investigated.

Oxygen flows-dependent photocatalytic performance in Ti3+ doped TiO2 thin films

Previous studies have found that Ti3+ plays a key role in the photocatalytic performance of TiO2. In this paper, we propose a cost-effective technique to realize the tunable photocatalytic activity in Ti3+ doped TiO2 thin films by simply varying oxygen flow during the case of deposition. The factors of oxygen flow and annealing temperature to the ratio of Ti3+ in TiO2 thin films were discussed. The results showed that both absorption in UV region and the yield of hydrogen from water splitting increased with the oxygen flow and annealing temperature decreasing.

Covalent bonding of ZnO nanostructures with dispersible carbon nanotubes for self-assembly photocatalytic heterostructures

Abstract This work demonstrates the fabrication of zinc oxide‑carbon nanotube (ZnO/CNT) heterostructures with tunable photocatalytic activity via microstructure modulation. The ZnO/CNT heterostructures are constructed in one-step hydrothermal procedure consisting of in situ anchoring of ZnO nanostructures with dispersible CNTs in an aqueous alkali solution containing bile salts as a dispersant. Observation via scanning (SEM) and transmission (TEM) electron microscopy reveals self-assembled heterostructures of monodispersible CNTs tightly surrounding ZnO nanostructures with multimorphology. The XRD, FT-IR, Raman and XPS analysis confirm that the CNTs were successfully incorporated into the ZnO nanostructures with strong interfacial contact of covalent bonding rather than simple mixing. A series of ZnO/CNT heterostructures, which varies according to their degree of doping with dispersible CNTs, exhibit distinct sunlight-induced photocatalytic activity onto the degradation of Rhodamine B (RhB). The superior photocatalytic performance of ZnO/CNT heterostructures originates from synergistic effects of sufficient interfacial bonding, self-assembly microstructures, and continuous conducting pathways between ZnO nanostructures and CNTs, which acquires better sunlight utilization and more efficient separation of electron-hole pair, confirmed by UV–Visible diffuse reflectance spectra as well as photocurrent and photovoltage analysis. This study also proposes a photocatalytic degradation mechanism of RhB dyes through detection of active species confirmed by electron-spin-resonance analysis.

Controllable synthesis and tunable photocatalytic activity of TiO2 nanowires via alcohol-thermal method

Titania nanowires (TiO2-NW) with tunable aspect ratios and morphologies were directly synthesized using a simple alcohol-thermal technique. Specifically, ethanol and acetic acid were used as solvents and lithium ion was used as the capping agent to promote the conversion of titanium butoxide into TiO2-NW. The morphologies and crystal phases of TiO2-NW were determined by the molar ratio of solvents and the content (mol%) of lithium ion. The band gap of TiO2-NW with pure anatase phase is slightly bigger than that of TiO2-NW with a mixture of anatase and rutile phases. All TiO2-NW could achieve effective decolorization of methyl blue (the decolorization rate is over 95%) after 35-min ultraviolet (UV) irradiation.

Harnessing designer biotemplates for biomineralization of TiO2 with tunable photocatalytic activity

Biomineralization is a promising material synthesis strategy for environmentally benign production of nanostructured metal oxides. An important question is whether biomineralization can be used in the biomimetic synthesis of TiO2 with tunable photocatalytic properties that are conducive to diverse solar energy conversion applications. Here, we report the biomineralization of energy-state-modified TiO2 nanoparticles, where the critical properties closely related to their photocatalytic activity can be manipulated by tailoring the nature of the designer biotemplates. For this purpose, STB1 heptapeptide was employed as a nucleation center to induce TiO2 biomineralization. Three distinctive types of biomolecules (peptide, protein, and phage) were deliberately designed to contain the STB1 nucleation core at different local densities and intermolecular distances. The degree of substitutional nitrogen-doping and the morphology are all subject to the context-dependent differential availability of STB1 in the biomineralization milieu. Phage-induced biomineralization results in TiO2 with modified energy state and wire-like network morphology, which account for significantly enhanced charge dissociation/transport performance and high photocatalytic activity. This is the first study to report that a specific peptide with biomineralizing activity exerts differential impacts on the properties of resulting biomineralization products in a context-dependent manner, and will provide a powerful new strategy for tailoring of material properties via biomineralization.

Peptide‐Templated Synthesis of TiO2 Nanofibers with Tunable Photocatalytic Activity

Nanofabrication based on biological templates has attracted considerable interest because of its applications in materials science and biomedicine. Herein, a facile method is reported for the synthesis of well-defined TiO2 nanofibers by using a simple N-(9-fluorenylmethoxycarbonyl)-protected phenylalanine-phenylalanine-aspartic acid tripeptide (Fmoc-Phe-Phe-Asp-OH, Fmoc-FFD) as the template. Compared with other synthetic methods of inorganic nanomaterials, these self-assembling peptides could control the structure and the catalytic activity of the synthesized nanomaterials produced under mild synthetic conditions. The as-synthesized peptide-TiO2 hybrid nanofibers and the calcined TiO2 nanofibers were characterized by using transmission electron microscopy (TEM), scanning electron microscopy (SEM), circular dichroism (CD) spectroscopy, and X-ray diffraction (XRD). The results show that well-defined TiO2 nanofibers could form when the pH of the peptide solution was 5-7, whereas nanoparticles formed when the pH was 8. Moreover, the peptide-templated TiO2 nanofibers showed improved photocatalytic activity for the degradation of methyl orange (MO). Finally, the photocatalytic activity of the TiO2 could be controlled by adjusting the pH of the peptide solution during the synthetic process.

Controlling the Core–Shell Structure of CuS@CdS Heterojunction via Seeded Growth with Tunable Photocatalytic Activity

We report the seed-mediated synthesis of CuS@CdS core–shell heterojunction with diverse morphologies by introducing kinetic control. By using CuS nanoplates as seeds and a collective manipulation of the injection rate of Cd2+ precursor with a syringe pump and the reaction temperature, two distinctive growth modes, i.e., island and layer-by-layer modes, respectively, could be realized. It is found that the growth is, in principle, determined by the deposition rate relative to the diffusion rate of the CdS growth monomers. Specifically, at a high injection rate and a relatively low reaction temperature, the deposition of CdS monomers on the surface of the CuS nanoplate follows an island growth mode because of the lattice mismatch between CuS and CdS and distinct binding energies of them. We can facilitate surface diffusion of these deposited monomers by reducing the injection rate of Cd2+ and increasing the reaction temperature. In this case, growth can be switched to a layer-by-layer mode. The products are...

Green controllable synthesis of Au–Ag alloy nanoparticles using Chinese wolfberry fruit extract and their tunable photocatalytic activity

Au–Ag alloy nanoparticles, synthesized using wolfberry fruit extract, showed linearly tunable photocatalytic activity through changing alloy composition and synthesis parameters.

Improving the photocatalytic H2 evolution activities of TiO2 by modulating the stabilizing ligands of the nanoscale Ti8O8-cluster precursors

Titanium-oxo clusters (TOCs) are important model complexes and potential precise single-source precursors of TiO2 materials. We report here a series of TiO2 samples derived from TOCs with the same wheel-like Ti8O8 clustercore but different stabilizing ligands. Our results demonstrate that the ligands on TOCs not only influence the phase-transition during themolysis, but more importantly tune the photocatalytic H2 evolution activities of the obtained TiO2 materials. Through 500 °C calcination, the nanosized Ti8O8 cluster stabilized by organic benzoate ligands gives rise to a TiO2 sample with H2 production rate of 611 μmol/h/g. When the stabilizing ligands are changed to inorganic SO42−, a significant improvement of H2 evolution activity has been achieved, resulting in a 7-times higher value of 4527 μmol/h/g. This work provides a new strategy to produce TiO2 with enhanced and tunable photocatalytic activities from titanium-oxo cluster precursors.

Controlled Growth of Metal-Organic Framework on Upconversion Nanocrystals for NIR-Enhanced Photocatalysis.

Development of MOF-based photocatalysts is intriguing research due to their structural flexibility and tremendous catalytic sites, whereas most MOFs only can take use of UV/visible light and lack of response to NIR light. Herein, we present a facile approach to integrate upconversion nanoparticles (UCNPs) with MOF to build a NIR-responsive composite photocatalyst. The MOF shell with controllable thickness can be grown on the UCNPs, thus exhibiting tunable photocatalytic activities under NIR irradiation. Furthermore, we extend visible absorption of the MOF shell by adding -NH2 groups so that the composite photocatalysts have a better utilization of UC emissions and sunlight to improve their activities. The developed composite photocatalysts have been characterized by XRD, TEM, PL, etc., and their photocatalytic performances were systematically explored. The formation and working mechanism of the composite photocatalysts were also elucidated.

Tunable Photocatalytic Activity of Palladium-Decorated TiO2: Non-Hydrogen-Mediated Hydrogenation or Isomerization of Benzyl-Substituted Alkenes

Palladium-decorated TiO2 is a moisture- and air-tolerant versatile catalyst. Its photocatalytic activity can be tuned in favor of hydrogenation or isomerization of benzyl-substituted alkenes simply by changing the irradiation wavelength. Benzyl-substituted alkenes are selectively isomerized to phenyl-substituted alkenes (E-isomer) with complete conversion over Pd@TiO2 under H2-free conditions. The reaction can be thermally induced under air or driven by visible-light irradiation at room temperature under Ar. UV irradiation in methanol solvent leads to efficient hydrogenation. The fine-tunability of the catalyst can also be used for selective deuterium incorporation using deuterated solvents; here H/D exchange is used as a mechanistic tool but with clear potential for isotope substitution applications.

High Efficiency Epitaxial‐Graphene/Silicon‐Carbide Photocatalyst with Tunable Photocatalytic Activity and Bandgap Narrowing

A novel way of tuning photocatalytic activity and bandgap narrowing in epitaxial graphene/silicon carbide (EG/SiC) yields high efficiency photocatalyst. Graphitization of SiC by high‐temperature thermal decomposition method with different annealing time forms sets of EG/SiC composites having different quality of graphene layers, confirmed by Raman spectroscopy. The Raman intensity ratio of the 2D band to the G band, I2D/IG, represents a measure of quality and quantity of graphene and heterojunction interface layer between EG and SiC. Experimental results reveal that I2D/IG plays a crucial role in tuning the bandgap and enhancement of photocatalytic activity of EG/SiC composites in a systematic manner irrespective of crystal structure or size of the SiC particles. In addition, EG/SiC shows intense broad background absorption in the visible range with increasing I2D/IG. The suitable selection of I2D/IG for EG/SiC gives excellent photocatalytic activity under UV light, up to ≈1000% enhancement and remarkable bandgap narrowing, upto 2 eV and even lesser, which is more than ≈30% reduction, relative to the as received SiC. The efficient control of the electronic structure in such EG/SiC heterojunctions obtained by tailoring the structural parameter I2D/IG opens up promising pathway for bandgap engineering and enhancement of photocatalytic activity.

Bi(1-x)La(x)CuSeO as New Tunable Full Solar Light Active Photocatalysts.

Photocatalysis is attracting enormous interest driven by the great promise of addressing current energy and environmental crises by converting solar light directly into chemical energy. However, efficiently harvesting solar energy for photocatalysis remains a pressing challenge, and the charge kinetics and mechanism of the photocatalytic process is far from being well understood. Here we report a new full solar spectrum driven photocatalyst in the system of a layered oxyselenide BiCuSeO with good photocatalytic activity for degradation of organic pollutants and chemical stability under light irradiation, and the photocatalytic performance of BiCuSeO can be further improved by band gap engineering with introduction of La. Our measurements and density-functional-theory calculations reveal that the effective mass and mobility of the carriers in BiCuSeO can be tuned by the La-doping, which are responsible for the tunable photocatalytic activity. Our findings may offer new perspectives for understanding the mechanism of photocatalysis through modulating the charge mobility and the effective mass of carriers and provide a guidance for designing efficient photocatalyts.