Surface Decoration of ZnWO₄ Nanorods with Cu₂O Nanoparticles to Build Heterostructure with Enhanced Photocatalysis

Pyto-Architechture of Ag, Au and Ag-Au bi-metallic nanoparticles using waste orange peel extract for enable carcinogenic Congo red dye degradation

Ecologically inspired to develop silver, gold and silver/gold bimetallic nanoparticles from discarded orange peel extract. The plant-derived compounds included in discarded orange peel extract have been accountable for the development of Ag, Au and Ag-Au bimetallic nanoparticles, that might be used in the biosynthetic process. The qualitative assessment of developed silver, gold and silver/gold bimetallic nanoparticles has been performed by UV-visible, XRD pattern, FT IR analysis, TEM/HRTEM, EDX and BET isotherm analysis. In this investigation, the photocatalytic effect of developed silver, gold and silver/gold bimetallic nanoparticles on Congo red dye breakdown efficiency was achieved at 96%, 94%, and 99.2%, respectively. Due to prolonged electron-hole recombination process was investigated using UV irradiation and reused for up to 5 consecutive runs without significant loss of photocatalytic activity. Moreover, silver, gold, and silver/gold bimetallic nanoparticles manufactured in an environmentally benign manner could potentially contribute to the ecological cleanup.

Fluorometric Sensing and Detection of p-Nitroaniline by Mixed Metal (Zn, Ni) Tungstate Nanocomposite

Aromatic amines are important chemical intermediates that hold an irreplaceable significance for synthesizing many chemical products. However, they may react with substances excreted from human bodies to generate blood poisoning, skin eczema, and dermatitis disease and even induce cancer-causing high risks to human health and the environment. Metal tungstates have been proven to be highly efficient materials for developing various toxic gases or chemical detection sensor systems. However, the major factors of the sensors, such as sensitivity, selectivity, stability, response, and recovery times, still need to be optimized for practical technological applications. In this work, Ni-doped ZnWO₄ mixed metal tungstate nanocomposite material was synthesized by the hydrothermal method and explored as a sensor for the fluorometric determination of p-nitroaniline (p-NA). Transmission electron microscopy (TEM) was used for the elucidation of the optimized particle diameter. Scanning electron microscopy (SEM) was employed to observe the surface morphological changes in the material during the solid-state reactions. The vibration modes of as-prepared samples were analyzed using Fourier-transform infrared spectroscopy (FTIR). The chemical bonding and oxidation states of individual elements involved in material synthesis were observed using X-ray photoelectron spectroscopy (XPS). The PL activities of the metal tungstate nanoparticles were investigated for the sensing of p-nitroaniline (p-NA). The obtained results demonstrated that ZnNiWO₄ was more effective in sensing p-NA than the other precursors were by using the quenching effect. The material showed remarkably high sensitivity towards p-NA in a concentration range of 25-1000 μM, and the limit of detection (LOD) value was found to be 1.93 × 10^-8 M for ZnWO₄, 2.17 × 10^-8 M for NiWO₄, and 2.98 × 10^-8 M for ZnNiWO₄, respectively.

A review on the applications of zinc tungstate (ZnWO4) photocatalyst for wastewater treatment

The monoclinic wolframite-phase structure of ZnWO₄ materials has been frequently synthesised, characterised, and applied in optical fibres, environmental decontamination, electrochemistry, photonics, catalysis, and not limited to magnetic applications. However, the problems of crystal growth conditions and mechanisms, growth, the crystal quality, stability, and the role of synthesis parameters of ZnWO₄ nanoparticles remain a challenge limiting its commercial applications. This review presents recent advances of ZnWO₄ as an advanced multi-functional material for Industrial wastewater treatment. The review also examines the influence of the synthesis parameters on the properties of ZnWO₄ and provides insight into new perspectives on ZnWO₄-based photocatalyst. Many researches have shown significant improvement in the efficiency of ZnWO₄ by mixing with polymers and doping with metals, nonmetals, and other nanoparticles. The review also provides information on the mechanism of doping ZnWO₄ with metals, non-metals, metalloids, metals oxides, and polymers based on different synthesis methods for bandgap reduction and extension of its photocatalytic activity to the visible region. The doped ZnWO₄ photocatalyst was a more effective and environmentally friendly material for removing organic and inorganic contaminants in industrial wastewater than ordinary ZnWO₄ nanocrystalline under suitable growth conditions.

Facile Synthesis of BiVO4@ZIF-8 Composite with Heterojunction Structure for Photocatalytic Wastewater Treatment

Water pollution has always been a serious problem across the world; therefore, facile pollutant degradation via light irradiation has been an attractive issue in the field of environmental protection. In this study, a type of Zn-based metal–organic framework (ZIF−8)-wrapped BiVO₄ nanorod (BiVO₄@ZIF−8) with high efficiency for photocatalytic wastewater treatment was synthesized through a two-step hydrothermal method. The heterojunction structure of BiVO₄@ZIF−8 was confirmed by morphology characterization. Due to the introduction of mesoporous ZIF−8, the specific surface area reached up to 304.5 m²/g, which was hundreds of times larger than that of pure BiVO₄ nanorods. Furthermore, the band gap of BiVO₄@ZIF−8 was narrowed down to 2.35 eV, which enabled its more efficient utilization of visible light. After irradiation under visible light for about 40 min, about 80% of rhodamine B (RhB) was degraded, which was much faster than using pure BiVO₄ or other BiVO₄-based photocatalysts. The synergistic photocatalysis mechanism of BiVO₄@ZIF−8 is also discussed. This study might offer new pathways for effective degradation of wastewater through facile design of novel photocatalysts.

CdS quantum dots-decorated InOOH: Facile synthesis and excellent photocatalytic activity under visible light

For the first time, CdS quantum dots (QDs)-decorated InOOH (CdS-In for short) was synthesized by a facile photodeposition method. The experiment results showed that CdS-In samples exhibited excellent activity and stability towards photocatalytic reduction of nitro aromatics. The conversion ratio of 4-nitroaniline (4-NA) over CdS-In sample that was prepared with photodeposition time of 120 min (CdS-In-120) reached up to 99.4% under visible light irradiation for 40 min, which was even higher than that achieved over commercial CdS (86.2%). Besides the significant enhancement of visible light absorption, quantum sized CdS were decorated evenly on the surface of InOOH, which was very beneficial for the high activity. Furthermore, the heterogeneous junction formed at the interface of CdS QDs and InOOH can significantly increase the separation efficiency of photogenerated charge carriers. Active species control experiment and electron spin resonance (ESR) technique have proved that photogenerated electrons are the main active species towards photocatalytic reduction of nitro aromatics. It is anticipated that our study would offer meaningful insights for exploring novel InOOH-based visible light photocatalysts towards efficient reduction of nitro aromatics.

Synthesis of ZnO nanoparticles using peels of Passiflora foetida and study of its activity as an efficient catalyst for the degradation of hazardous organic dye

Creating a sustainable and effective approach to handling organic contaminants from industrial waste is an ongoing problem. In the present study, ZnO nanoparticles (ZnO NPs) were synthesized under a controlled ultrasound cavitation technique using the extract of Passiflora foetida fruit peels, which act as a reducing (i.e., reduction of metal salt) and stabilizing agent. The formation of monodispersed and hexagonal morphology (average size approximately 58 nm with BET surface area 30.83m2/g). The synthesized ZnO NPs were characterized by a various technique such as UV–visible spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared (FTIR), Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Transmission electron microscopy (TEM), Thermogravimetric analysis (TGA) and Dynamic light scattering (DLS). Further, the XRD pattern confirmed the hexagonal wurtzite structure of synthesized ZnONPs. The ZnO NPs exhibit excellent degradation efficiency towards organic pollutant dyes, i.e., Methylene blue (MB) (93.25% removal) and Rhodamine B (91.06% removal) in 70 min, under natural sunlight with apparent rate constant 0.0337 min−1 (R2 = 0.9749) and 0.0347 min−1 (R2 = 0.9026) respectively.Zeta potential study shows the presence of a negative charge on the surface of ZnO NPs. The use of green synthesized ZnO NPs is a good choice for wastewater treatment, given their high reusability and photocatalytic efficiency, along with adaptability to green synthesis.

Recent advances in Cu2O-based composites for photocatalysis: a review

Cu₂O-based composites for photocatalysis have been extensively explored owing to their promising application in solving environmental and energy problems. At present, the research on photocatalysis is focused on improving the photocatalytic performance of materials. It has been reported that adjusting the morphology and size of Cu₂O can effectively improve its photocatalytic property. However, photocorrosion is still an inevitable problem, which hinders the application of Cu₂O in photocatalysis. The strategies of constructing heterogeneous nanostructures and ion doping can significantly improve the light stability, light absorption capacity and separation efficiency of electron-hole pairs. Cu₂O-based composites exhibit superior performances in degrading organic matter, producing hydrogen, reducing CO₂ and sterilization. Therefore, the construction of multi-materials will be one of the future directions in their photocatalytic application. This review summarizes the recent strategies for enhancing the photocatalytic activity of Cu₂O by analyzing different Cu₂O-based photocatalysts, and the charge transfer pathway is further discussed in detail. Finally, several opportunities and challenges in the field of photocatalysis are illustrated.

Fe-Doped g-C3N4: High-Performance Photocatalysts in Rhodamine B Decomposition

Herein, Fe-doped C3N4 high-performance photocatalysts, synthesized by a facile and cost effective heat stirring method, were investigated systematically using powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface area measurement, X-ray photoelectron (XPS), UV-Vis diffusion reflectance (DRS) and photoluminescence (PL) spectroscopy. The results showed that Fe ions incorporated into a g-C3N4 nanosheet in both +3 and +2 oxidation states and in interstitial configuration. Absorption edge shifted slightly toward the red light along with an increase of absorbance in the wavelength range of 430-570 nm. Specific surface area increased with the incorporation of Fe into g-C3N4 lattice, reaching the highest value at the sample doped with 7 mol% Fe (FeCN7). A sharp decrease in PL intensity with increasing Fe content is an indirect evidence showing that electron-hole pair recombination rate decreased. Interestingly, Fe-doped g-C3N4 nanosheets present a superior photocatalytic activity compared to pure g-C3N4 in decomposing RhB solution. FeCN7 sample exhibits the highest photocatalytic efficiency, decomposing almost completely RhB 10 ppm solution after 30 min of xenon lamp illumination with a reaction rate approximately ten times greater than that of pure g-C3N4 nanosheet. This is in an agreement with the BET measurement and photoluminescence result which shows that FeCN7 possesses the largest specific surface area and low electron-hole recombination rate. The mechanism of photocatalytic enhancement is mainly explained through the charge transfer processes related to Fe2+/Fe3+ impurity in g-C3N4 crystal lattice.

Solid solution ZnW1−xMoxO4 for enhanced photocatalytic H2 evolution

ZnW_1−xMo_xO₄ and n–n heterojunction ZnW_1−xMo_xO₄/CdS complexes exhibited photocatalytic hydrogen evolution activity superior to that of pristine ZnWO₄.

Enhanced Visible-Light Photocatalytic Activity of Ag QDs Anchored on CeO2 Nanosheets with a Carbon Coating

Ag quantum dots (QDs) anchored on CeO₂ nanosheets with a carbon coating (Ag/CeO₂@C) (composites) were prepared via an in situ reduction approach for the photocatalytic degradation of Cr(VI) and tetracycline hydrochloride (TCH) in the visible-light region. The photocatalytic activity of Ag/CeO₂@C was greatly affected by carbon content, Ag-doping content, Cr(VI) concentration, pH value, and inorganic ions. Enhanced photocatalytic activity was obtained by Ag/CeO₂@C (compared to CeO₂ and CeO₂@C), of which 3-Ag/CeO₂@C-2 with an Ag-doping content of 5.41% presented the best removal efficiency and the most superior stability after five cycles. ·O₂⁻ and ·OH radicals were crucial for the photocatalytic capacity of 3-Ag/CeO₂@C-2. The combined effect of the surface plasma resonance (SPR) of Ag QDs, an electron trapper of carbon shells, and the redox activity of the Ce(III)/Ce(IV) coupling induced efficient charge transfer and separation, suppressing the recombination of electron–hole pairs.

CuInS2/Mg(OH)2 Nanosheets for the Enhanced Visible-Light Photocatalytic Degradation of Tetracycline

CuInS₂/Mg(OH)₂ (CIS/Mg(OH)₂) nanosheets have been prepared for the visible light activated photodegradation of tetracycline hydrochloride (TCH). The introduction of CuInS₂ has proven to enhance the photocatalytic activity of Mg(OH)₂ nanosheets. It’s ascribed to the enhanced transfer and separation of charge carriers at the junction interface between CuInS₂ and Mg(OH)₂. The photocatalytic activity of obtained CIS/Mg(OH)₂ is greatly affected by CuInS₂ content, pH value, and inorganic ions. Among these samples, 2-CIS/Mg(OH)₂ exhibits the excellent photocatalytic activity and durability for the visible light driven removal of TCH after five cycle times. Atomic force microscope (AFM) images indicate that the surface roughness of 2-CIS/Mg(OH)₂ is intensively influenced in adsorption-photocatalysis process. The •O₂⁻ and •OH radicals are vital for the visible light driven photocatalytic activity of 2-CIS/Mg(OH)₂ for TCH removal.

Continuously Improved Photocatalytic Performance of Zn2SnO4/SnO2/Cu2O Composites by Structural Modulation and Band Alignment Modification

Improving the photocatalytic performance of multi-component photocatalysts through structural modulation and band alignment engineering has attracted great interest in the context of solar energy utilization and conversion. In our work, Zn₂SnO₄/SnO₂ hierarchical architectures comprising nanorod building block assemblies were first achieved via a facile solvothermal synthesis route with lysine and ethylenediamine (EDA) as directing agents, and then chemically etched in NaOH solution to enlarge the surface area and augment active sites. The etched Zn₂SnO₄/SnO₂ hierarchical architectures were further decorated by Cu₂O nanoparticles though an in situ chemical deposition method based on band alignment engineering. In comparison with unetched Zn₂SnO₄/SnO₂, the specific surface area of Zn₂SnO₄/SnO₂/Cu₂O hierarchical architectures became larger, and the responsive region and absorbance intensity became wider and higher in the whole visible-light range. Zn₂SnO₄/SnO₂/Cu₂O hybrid photocatalysts presented enormously improved visible-light photocatalytic behaviour for Rhodamine B (RhB) decomposition. The enhancement of photocatalytic behaviour was dominantly attributed to the synergy effect of the larger specific surface area, higher light absorption capacity, and more effective photo-induced charge carrier separation and migration. A proposed mechanism for the enormously promoted photocatalytic behaviour is brought forth on the basis of the energy-band structure combined with experimental results.

Enhancement of Photocatalytic Activity under Visible Light Irradiation via the AgI@TCNQ Core-Shell Structure

In this paper, a AgI@TCNQ photocatalyst with a core-shell structure was reported. A two-dimensional TCNQ (7,7,8,8-Tetracyanoquinodimethane) nanosheet, with a π-π conjugate structure, was used as a shell layer to realize the flexible coating on the surface of AgI nanoparticles. These special core-shell structure composites solve the key problems of the small interface of the bulk composites and the lesser charge transfer paths, which could accelerate the migration of photogenerated carriers. Thus, the AgI@TCNQ photocatalysts showed the better photodegradation performance for the methylene blue (MB) solution, and the degradation rate of AgI@TCNQ (1 wt.%) composite was 1.8 times than AgI under irradiation. The reactive species trapping experiments demonstrated that ·O2-, h+, and ·OH all participated in the MB degradation process. The photocatalytic mechanism of AgI@TCNQ composites could be rationally explained by considering the Z-scheme structure, resulting in a higher redox potential and more efficient separation of charge carriers. At the same time, the unique core-shell structure provides a larger contact area, expands the charge transport channel, and increases the surface active sites, which are beneficial for improving photocatalytic performance.

Strong Photo-Oxidative Capability of ZnWO4 Nanoplates with Highly Exposed {0 1 1} Facets

ZnWO4 nanoplates with highly exposed {0 1 ¯ 1} facets were synthesized via a hydrothermal technique. The phase, morphology, and optical characteristics of ZnWO4 nanoplates were characterized with scanning electron microscopy, transmission electron microscopy, X–ray diffraction, diffuse ultraviolet–visible light (UV–Vis) reflectance spectroscopy, photoluminescence (PL) spectrophotometry, and PL lifetime spectroscopy. Optical characterizations, along with the density functional calculations, confirm that the strong blue PL band of ZnWO4 nanoplates originates from the intrinsic defects in ZnWO4 nanoplates. Furthermore, photocatalytic tests show that ZnWO4 nanoplates exhibit strong photo-oxidative capability of complete mineralization of the organic pollutant (methyl orange) in water, whereas ZnWO4 nanoparticles can only cleave the organic molecules into fragments. The superior photo-oxidative capability of ZnWO4 nanoplates can be attributed to the specific chemical bonding and stereochemistry on the exposed facets. This work demonstrates that crystal facet engineering is an efficient strategy to endow ZnWO4 with strong photo-oxidative capability.

Eu2+ and Eu3+ Doubly Doped ZnWO₄ Nanoplates with Superior Photocatalytic Performance for Dye Degradation

Eu²⁺ and Eu³⁺ doubly doped ZnWO₄ nanoplates with highly exposed {100} facets were synthesized via a facile hydrothermal route in the presence of surfactant cetyltrimethyl ammonium bromide. These ZnWO₄ nanoplates were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, diffuse UV-vis reflectance spectroscopy, photoluminescence spectrophotometry, and photoluminescence lifetime spectroscopy to determine their morphological, structural, chemical, and optical characteristics. It is found that Eu-doped ZnWO₄ nanoplates exhibit superior photo-oxidative capability to completely mineralize the methyl orange into CO₂ and H₂O, whereas undoped ZnWO₄ nanoparticles can only cleave the organic molecules into fragments. The superior photocatalytic performance of Eu-doped ZnWO₄ nanoplates can be attributed to the cooperative effects of crystal facet engineering and defect engineering. This is a valuable report on crystal facet engineering in combination with defect engineering for the development of highly efficient photocatalysts.

Extended Near-Infrared Photoactivity of Bi₆Fe1.9Co0.1Ti₃O18 by Upconversion Nanoparticles

Bi₆Fe_1.9Co_0.1Ti₃O₁₈ (BFCTO)/NaGdF₄:Yb³⁺, Er³⁺ (NGF) nanohybrids were successively synthesized by the hydrothermal process followed by anassembly method, and BFCTO-1.0/NGF nanosheets, BFCTO-1.5/NGF nanoplates and BFCTO-2.0/NGF truncated tetragonal bipyramids were obtained when 1.0, 1.5 and 2.0 M NaOH were adopted, respectively. Under the irradiation of 980 nm light, all the BFCTO samples exhibited no activity in degrading Rhodamine B (RhB). In contrast, with the loading of NGF upconversion nanoparticles, all the BFCTO/NGF samples exhibited extended near-infrared photoactivity, with BFCTO-1.5/NGF showing the best photocatalytic activity, which could be attributed to the effect of {001} and {117} crystal facets with the optimal ratio. In addition, the ferromagnetic properties of the BFCTO/NGF samples indicated their potential as novel, recyclable and efficient near-infrared (NIR) light-driven photocatalysts.

Facet-Dependent Cuprous Oxide Nanocrystals Decorated with Graphene as Durable Photocatalysts under Visible Light

Three morphologies (octahedral, hierarchical and rhombic dodecahedral) of crystal Cu₂O with different facets ({111}, {111}/{110}, and {110}) incorporating graphene sheets (denoted as o-Cu₂O-G, h-Cu₂O-G and r-Cu₂O-G, respectively) have been fabricated by using simple solution-phase techniques. Among these photocatalysts, the r-Cu₂O-G possesses the best photocatalytic performance of 98% removal efficiency of methyl orange (MO) with outstanding kinetics for 120 min of visible light irradiation. This enhancement is mainly due to the dangling “Cu” atoms in the highly active {110} facets, resulting in the increased adsorption of negatively charged MO. More importantly, the unique interfacial structures of Cu₂O rhombic dodecahedra connected to graphene nanosheets can not only decrease the recombination of electron-hole pairs but also stabilize the crystal structure of Cu₂O, as verified by a series of spectroscopic analyses (e.g., X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM)). The effective photocatalysts developed in this work could be applied to the efficient decolorization of negatively charged organic dyes by employing solar energy.

Fast photocatalytic degradation of dyes using low-power laser-fabricated Cu2O–Cu nanocomposites

Facile synthesis of Cu₂O–Cu nanocomposites by using a low-power CO₂laser was realized, and the fabricated nanomaterials showed excellent photocatalytic activity for the degradation of various dyes.