Furfural-induced hydrothermal synthesis of ZnO@C gemel hexagonal microrods with enhanced photocatalytic activity and stability

Cotton-derived three-dimensional carbon fiber aerogel with hollow nanocapsules and ultrahigh adsorption efficiency in dynamic sewage treatment system

An ultralight 3D carbon fiber aerogel with good flexibility is developed via soaking cotton in water and then calcinating at a high temperature. This cotton-derived carbon material is constituted by amorphous carbon and retains slight oxygen-containing groups. Besides, a lot of hollow carbon nanocapsules are yielded on the inside surface, resulting in abundant micropores and mesopores. Systemic investigations explore the molecular transformation from cotton to carbon fiber, and the formation of carbon nanocapsules. In the adsorption process for methyl orange (MO), this carbon fiber aerogel exhibits both a rapid adsorption rate and the ultrahigh adsorbability of 862.9 mg/g, outclassing most of carbon materials reported. Therefore, a dynamic sewage treatment system is built and consecutively removes hydrosoluble pollution for a long-term running time. For the cotton-derived carbon fiber aerogel, the good mechanical flexibility, excellent adsorption property, and high stability jointly provide a vast application prospect in future industrial wastewater remediation.

Solvothermal Synthesis of ZnO Nanoparticles for Photocatalytic Degradation of Methyl Orange and p-Nitrophenol

The photocatalytic degradation of organic pollutants is an effective method of controlling environmental pollution. ZnO nanoparticles (ZnO NPs) were prepared by the solvothermal method and characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–visible diffuse reflectance spectroscopy (UV–Vis DRS). The results showed that the ZnO NPs had a uniform size of 25–40 nm, hexagonal wurtzite structure, and a band gap of 2.99 eV. The photocatalytic degradation of methyl orange (MO) and p-nitrophenol (PNP) was used as a model reaction to evaluate the photocatalytic activity of ZnO NPs. The photocatalytic degradation rates (pseudo-first-order kinetics) of MO and PNP were 92% (0.0128 min−1) and 56.2% (0.0042 min−1), respectively, with a 25 W ultraviolet lamp, MO/PNP concentration = 20 mg/L, ZnO NPs dose = 1.5 g/L, and time = 180 min. The photocatalytic mechanism of ZnO NPs and degradation pathways of MO and PNP were also proposed. The results provide valuable information and guidance for the treatment of wastewater via photocatalytic methods.

Visible-Light-Responsive Photocatalytic Activity Significantly Enhanced by Active [VZn+VO+] Defects in Self-Assembled ZnO Nanoparticles

Defect influences on the photoactivity of ZnO nanoparticles prepared by a powdered coconut water (ACP) assisted synthesis have been studied. The crystalline phase and morphology of ZnO nanoparticles were effectively controlled by adjusting the calcination temperature (400-700 °C). An induced transition of hybrid Zn₅(CO₃)₂(OH)₆/ZnO nanoparticles to single-phase ZnO nanoparticles was obtained at 480 °C. The morphological analysis revealed a formation of ZnO nanoparticles with semispherical (∼6.5 nm)- and rod-like (∼96 nm) shapes when the calcination temperatures were 400 and 700 °C, respectively. Photoluminescence characterizations revealed several defects types in the samples with V_Zn and V_O⁺ being in the self-assembly of semispherical- and rod-like ZnO nanoparticles. The photocatalytic activity of the ZnO nanoparticles was examined by assessing the degradation of methylene blue in an aqueous solution under low-intensity visible-light irradiation (∼3 W m^-2). The results point toward the self-assembly of semispherical- and rod-like ZnO nanoparticles that had significantly better photocatalytic activity (∼31%) in comparison to that of spherical-agglomerated- or near-spherical-like species within 120 min of irradiation. The possible photocatalytic mechanism is discussed in detail, and the morphology-driven intrinsic [V_Zn+V_O⁺] defects are proposed to be among the active sites of the ZnO nanoparticles enhancing the photocatalytic activity.

Fabrication of Mesoporous PtO-ZnO Nanocomposites with Promoted Photocatalytic Performance for Degradation of Tetracycline

Herein, we report a simple incorporation of PtO NPs at diverse percentages (0.2-0.8 wt %) onto a highly crystalline and mesoporous ZnO matrix by the wet-impregnation approach for degradation of tetracycline (TC) upon visible light exposure. These well-dispersed and small-sized PtO NPs provide the mesoporous PtO-ZnO nanocomposites with outstanding photocatalytic performance for complete TC degradation. The optimized 0.6% PtO-ZnO photocatalyst exhibits excellent TC degradation, and its degradation efficiency reached ∼99% within 120 min. The photocatalytic performance of the 0.6% PtO-ZnO nanocomposite is 20 and 10 times higher than that of pristine ZnO and commercial P-25, respectively. The photodegradation rate of TC over the 0.6% PtO-ZnO nanocomposite is 34 and 12.5 times greater than that of pristine ZnO and commercial P-25, respectively. This is because of the large surface area, unique porous structure, synergistic effect, and broad visible light absorption of the PtO-ZnO nanocomposite. Moreover, mesoporous PtO-ZnO nanocomposites showed a high stability and recyclability over five iterations. This work demonstrates the remarkable role of combining PtO and ZnO photocatalysts in providing nanocomposites with significant potential for the preservation of human health through wastewater remediation.

One-step hydrothermal synthesis of hierarchical nanosheet-assembled Bi2O2CO3 microflowers with a {001} dominant facet and their superior photocatalytic performance

Using citric acid (CA) and 1,5-naphthalenedisulfonic acid (NDSA) as the structure-directing agent, a hierarchical flower-like Bi₂O₂CO₃ product is successfully prepared via a simple one-step hydrothermal synthesis, which is spirally assembled by the {001} facet-dominated nanosheets. It is testified that the additive CA plays an important inducing role in forming the chemical composition of Bi₂O₂CO₃, the nanosized sheet-type subunits, and the exposure of the {001} facet, while the NDSA greatly improves the dispersity and porous structure of the Bi₂O₂CO₃ microflower. Due to the nano-size effect and distortion of surface Bi-O bonds, the Bi₂O₂CO₃ microflower could be excited by the visible light to exhibit a superior photocatalytic performance in the degradation of tetracycline (TC). Besides, it is found the exposed {001} facet of Bi₂O₂CO₃ would preferentially generate holes during the illumination process, thus enhancing the photooxidative activity of the Bi₂O₂CO₃ microflower. Finally, the structural and optical features of the Bi₂O₂CO₃ microflower have been discussed in detail, and its photocatalytic mechanism has also been proposed in this work.

Preparation of carbon-coated brookite@anatase TiO2 heterophase junction nanocables with enhanced photocatalytic performance

One-dimensional TiO2@C nanocables with a heterophase junction have been successfully prepared by coating brookite@anatase TiO2 with a thin layer of hydrothermal carbon (HTC). Compared with anatase TiO2, the biphase brookite@anatase structure can reduce the recombination rate of the excited electron/hole pairs of TiO2. The HTC coating not only enhances the adsorption capability of the TiO2 catalyst for organic pollutants but also facilitates photogenerated electron transfer to further increase its photocatalytic activity. Therefore, compared with anatase TiO2, brookite@anatase TiO2, and TiO2@C, the brookite@anatase TiO2@C shows the highest photocatalytic activity for the photodegradation of tetracycline (TC) under the irradiation of UV-visible light. Moreover, ˙O2 has been proved to be the predominant active species for the photodegradation of TC, and the photocatalytic mechanism of brookite@anatase TiO2@C nanocables has also been proposed.

Formation of Lattice-Dislocated Zinc Oxide via Anodic Corrosion for Electrocatalytic CO2 Reduction to Syngas with a Potential-Dependent CO:H2 Ratio

The electrochemical reduction of CO₂ and H₂O to syngas, a widely used precursor for chemical synthesis, has attracted increased attention. However, producing syngas over a wide range of CO:H₂ ratios is important for its potential application. Herein, a facile method using an anodic oxidizing zinc plate has been developed to obtain lattice-dislocated ZnO, which exhibited higher faradaic efficiencies (above 90%) of syngas than that of ZnO without lattice dislocation. Moreover, the ratio of CO to H₂ can be regulated in a wide range from 0.28 to 2.11 by applying different electrolyzing potentials, which is applicable to the synthesis of various chemicals. With density functional theory calculations, we conclude that the lattice dislocation defects in ZnO promote the electroreduction of CO₂. In addition, stability and electrochemical noise tests show that lattice-dislocated ZnO can withstand long-term operation due to its effective corrosion resistance.

Recent Development of Photocatalysts Containing Carbon Species: A Review

Undoubtedly, carbon-based (nano)composites can be promising photocatalysts with improved photocatalytic activity due to the coupling effect from the incorporation of carbon species. In this mini-review, we focus on the recent development of photocatalysts based on carbon-based (nano)composites. TiO2 is well-known as a typical photocatalyst. Special attention is paid to the various types of carbon–TiO2 composites such as C-doped TiO2, N–C-doped TiO2, metal–C-doped TiO2, and other co-doped C/TiO2 composites. Various synthetic strategies including the solvothermal/hydrothermal method, sol–gel method, and template-directed method are reviewed for the preparation of carbon-based TiO2 composites. C/graphitic carbon nitride (g-C3N4) composites and ternary C-doped composites are also summarized and ascribed to the unique electronic structure of g-C3N4 and the synergistic effect of the ternary interfaces, respectively. In the end, we put forward the future perspective of the photocatalysts containing carbon species based on our knowledge.

Photoinduced in Situ Deposition of Uniform and Well-Dispersed PtO2 Nanoparticles on ZnO Nanorods for Efficient Catalytic Reduction of 4-Nitrophenol

Based on the photochemical property of semiconductors, a light irradiation-assisted strategy has been designed using one-dimensional ZnO nanorods as carriers to synthesize the rod-type PtO₂/ZnO catalyst with a well-defined structure. The high crystallinity and uniform crystal structure of the ZnO matrix conduct the in situ deposition of PtO₂ nanoparticles with 1.1-2.1 nm, which are evenly and densely anchored on the surface. Those small-sized and well-dispersed PtO₂ nanoparticles endow the PtO₂/ZnO catalyst a superior catalytic performance for the reduction of 4-nitrophenol to 4-aminophenol, which can convert all the substrates within 6.25 min. It is demonstrated that the catalytic activity of the PtO₂/ZnO catalyst is 2.3 times as high as that of the sample obtained by traditional wet-oxidation method under the same reaction conditions. Moreover, the light-irradiation time has been found to greatly affect the structure and activity of PtO₂/ZnO catalysts, and the product with 30 min exhibits the best catalytic performance in this work, as well as the good stability for ten runs. In terms of the photoexcited process of ZnO and reactive species-trapped experiments, the formation mechanism of PtO₂/ZnO catalysts has been explored in detail, which will probably stimulate the design and study of other metal-supported catalysts.

Synthesis, Characterization, and Photocatalytic Properties of Bamboo Charcoal/TiO₂ Composites Using Four Sizes Powder

Visible-light-active bamboo biochar/TiO₂ composites were fabricated by the calcination method using C₁₆H₃₆O₄Ti as the titanium source and bamboo powder with different sizes as the carbon source. The TiO₂ nanoparticles were observed to disperse onto the surface of bamboo biochar fiber. The sizes of the bamboo powder played an important role in the microstructures and the properties of bamboo biochar/TiO₂ composites. The bamboo biochar/TiO₂ composites displayed the photocatalytic activities both under visible light irradiation and UV irradiation. The adsorption isotherms better fitted Freundlich isotherm models and the photodegradation reactions followed pseudo-first-order kinetics. Bamboo charcoal/TiO₂ composites exhibited high stability after up to four cycles. This research could pave the way for high-value applications of biomass in the environmental field.

Diethylenediamine-assisted template-free synthesis of a hierarchical TiO2 sphere-in-sphere with enhanced photocatalytic performance

With the assistance of DETA, a template-free solvothermal approach is employed to synthesize a hierarchical TiO₂ sphere-in-sphere with enhanced photocatalytic performance.

Ag-CuO-ZnO metal-semiconductor multiconcentric nanotubes for achieving superior and perdurable photodegradation

Solar energy represents a robust and natural form of resource for environment remediation via photocatalytic pollutant degradation with minimum associated costs. However, due to the complexity of the photodegradation process, it has been a long-standing challenge to develop reliable photocatalytic systems with low recombination rates, excellent recyclability, and high utilization rates of solar energy, especially in the visible light range. In this work, a ternary hetero-nanostructured Ag-CuO-ZnO nanotube (NT) composite is fabricated via facile and low-temperature chemical and photochemical deposition methods. Under visible light irradiation, the as-synthesized ZnO NT based ternary composite exhibits a greater enhancement (∼300%) of photocatalytic activity than its counterpart, Ag-CuO-ZnO nanorods (NRs), in pollutant degradation. The enhanced photocatalytic capability is primarily attributed to the intensified visible light harvesting, efficient charge carrier separation and much larger surface area. Furthermore, our as-synthesised hybrid ternary Ag-CuO-ZnO NT composite demonstrates much higher photostability and retains ∼98% of degradation efficiency even after 20 usage cycles, which can be mainly ascribed to the more stable polar planes of ZnO NTs than those of ZnO NRs. These results afford a new route to construct ternary heterostructured composites with perdurable performance in sewage treatment and photocorrosion suppression.

Pt/ZnO@C Nanocable with Dual-Enhanced Photocatalytic Performance and Superior Photostability

To improve the photocatalytic activity and photostability of ZnO, a novel cable-like Pt/ZnO@C composite is successfully fabricated by coating a 3-5 nm hydrothermal carbon (HTC) layer on the surface of the Pt nanoparticle-modified ZnO nanowire. After investigating the optical and photoelectrochemical performance in detail, it is found that the Pt/ZnO@C nanocable shows a dual-enhanced migration efficiency for the photoinduced surface electrons, distributing to the modified Pt nanoparticles and the coated HTC layer. Consequently, the Pt/ZnO@C nanocable exhibits a dual-enhanced photocatalytic activity for the degradation of various organic pollutants under the UV light irradiation. The coated HTC layer can also play a role in suspending the ZnO photocorrosion and significantly improves the photostability of the Pt/ZnO@C nanocable. Furthermore, the photocatalysis and photocorrosion mechanism of the Pt/ZnO@C nanocable is proposed and discussed in terms of its structural feature and photoelectrochemical property. The resultant Pt/ZnO@C nanocable with the unique HTC layer-coated structure will probably stimulate to design and synthesize more HTC-hybridized composites with a superior photocatalytic or photoelectrocatalytic performance.

Diethylenetriamine-assisted in situ synthesis of TiO2 nanoparticles on carbon nanotubes with well-defined structure and enhanced photocatalytic performance

In solvothermal conditions, DETA will work as a connecting bridge to in situ form TiO₂/CNT composites with a well-defined structure and enhanced photocatalytic performance.

B. RK, Jones LA, Mayes ELH, Ippolito SJ, Sunkara MV. Modulating interleaved ZnO assembly with CuO nanoleaves for multifunctional performance: perdurable CO2 gas sensor and visible light catalyst

Efficient CO₂ gas detection and visible light photocatalysis performance shown by interleaved CuO/ZnO heterostructures ascribed primarily to the high surface area, p/n nano-interfaces and catalytic role of Ag.

Graphene quantum dots modified ZnO + Cu heterostructure photocatalysts with enhanced photocatalytic performance

GQDs surface modified ZnO + Cu heterostructure photocatalysts was prepared via a simple spin-coating and annealing process, which exhibits enhanced photocatalytic performance.

Facile fabrication of highly efficient modified ZnO photocatalyst with enhanced photocatalytic, antibacterial and anticancer activity

Photocatalytic degradation of organic pollutants using hexagonal Er and Nd doped ZnO photocatalyst.

Glucose-assisted transformation of Ni-doped-ZnO@carbon to a Ni-doped-ZnO@void@SiO2 core–shell nanocomposite photocatalyst

Nanovoid core–shell structured Ni/ZnO@void@SiO₂ was obtained using the carbon layer of Ni/ZnO@C as a sacrificial template.

Mass preparation and novel visible light photocatalytic activity of C and Ag Co-modified ZnO nanocrystals

A combustion method was developed to synthesize the C and Ag co-modified ZnO NCs to enhance its photocatalytic efficiency and practicability. The results showed that the doped Ag was significant to promote the photocatalytic activity, and the optimum content was 2% molar ratio of Ag to Zn atom. The degradation rate under visible light increased by 150% compared with C-ZnO NCs, while by more 1233.3% than pure ZnO photocatalyst. There were some new little particles with grain size about 10 nm on the C-ZnO NCs surface, which may state for the existence of Ag atoms. The synergy effect of Ag and carbon elements was proposed to explain the mechanism of enhanced photocatalytic performance under visible light irradiation.

A novel method for furfural recovery via gas stripping assisted vapor permeation by a polydimethylsiloxane membrane

Furfural is an important platform chemical with a wide range of applications. However, due to the low concentration of furfural in the hydrolysate, the conventional methods for furfural recovery are energy-intensive and environmentally unfriendly. Considering the disadvantages of pervaporation (PV) and distillation in furfural separation, a novel energy-efficient ‘green technique’, gas stripping assisted vapor permeation (GSVP), was introduced in this work. In this process, the polydimethylsiloxane (PDMS) membrane was prepared by employing water as solvent. Coking in pipe and membrane fouling was virtually non-existent in this new process. In addition, GSVP was found to achieve the highest pervaporation separation index of 216200 (permeate concentration of 71.1 wt% and furfural flux of 4.09 kgm⁻²h⁻¹) so far, which was approximately 2.5 times higher than that found in pervaporation at 95°C for recovering 6.0 wt% furfural from water. Moreover, the evaporation energy required for GSVP decreased by 35% to 44% relative to that of PV process. Finally, GSVP also displayed more promising potential in industrial application than PV, especially when coupled with the hydrolysis process or fermentation in biorefinery industry.

Monolithic organic/inorganic ternary nanohybrids toward electron transfer cascade for enhanced visible-light photocatalysis

Monolithic organic/inorganic ternary nanohybrids were facilely prepared toward electron transfer cascade and demonstrated enhanced visible-light photocatalytic activity.

Sequential growth of zinc oxide nanorod arrays at room temperature via a corrosion process: application in visible light photocatalysis

Many photocatalyst systems catalyze chemical reactions under ultraviolet (UV) illumination, because of its high photon energies. Activating inexpensive, widely available materials as photocatalyst using the intense visible part of the solar spectrum is more challenging. Here, nanorod arrays of the wide-band-gap semiconductor zinc oxide have been shown to act as photocatalysts for the aerobic photo-oxidation of organic dye Methyl Orange under illumination with red light, which is normally accessible only to narrow-band semiconductors. The homogeneous, 800-1000-nm-thick ZnO nanorod arrays show substantial light absorption (absorbances >1) throughout the visible spectral range. This absorption is caused by defect levels inside the band gap. Multiple scattering processes by the rods make the nanorods appear black. The dominantly crystalline ZnO nanorod structures grow in the (0001) direction, i.e., with the c-axis perpendicular to the surface of polycrystalline zinc. The room-temperature preparation route relies on controlled cathodic delamination of a weakly bound polymer coating from metallic zinc, an industrially produced and cheaply available substrate. Cathodic delamination is a sequential synthesis process, because it involves the propagation of a delamination front over the base material. Consequently, arbitrarily large sample surfaces can be nanostructured using this approach.