Pristine and Graphene-Quantum-Dots-Decorated Spinel Nickel Aluminate for Water Remediation from Dyes and Toxic Pollutants

Graphene quantum dots incorporated NiAl2O4 nanocomposite based molecularly imprinted electrochemical sensor for 5-hydroxymethyl furfural detection in coffee samples

5-Hydroxymethyl furfural (HMF) is an intermediate produced by dehydrating sugars, such as fructose, sucrose, and glucose, in an acidic medium or during the Maillard reaction. It also occurs due to the storage of sugary foods at inappropriate temperatures. In addition, HMF is seen as a quality criterion in products. In this study, a novel molecularly imprinted electrochemical sensor based on graphene quantum dots incorporated NiAl₂O₄ (GQDs-NiAl₂O₄) nanocomposite was presented for the selective determination of HMF in coffee samples. Various microscopic, spectroscopic, and electrochemical methods were carried out for the structural characterizations of GQDs-NiAl₂O₄ nanocomposite. The molecularly imprinted sensor was prepared by multi-scanning using cyclic voltammetry (CV) in the presence of 100.0 mM pyrrole monomer and 25.0 mM HMF. After method optimization, the sensor revealed linearity towards HMF in the range of 1.0-10.0 ng L^-1 with a detection limit (LOD) of 0.30 ng L^-1. The developed MIP sensor's high repeatability, selectivity, stability, and fast response ability can provide reliable HMF detection in beverages, such as coffee, which is heavily consumed.

Facile Preparation of a Novel Bi2WO6/Calcined Mussel Shell Composite Photocatalyst with Enhanced Photocatalytic Performance

The exploration of cost-effective and highly efficient photocatalysts is still a great challenge. In this work, a cost-effective and highly active Bi2WO6/calcined mussel shell (CMS/BWO) composite photocatalyst was prepared by a facile solvothermal route, in which Bi2WO6 nanosheets were tightly, evenly, and vertically grown on waste calcined mussel shells (CMS). Multiple techniques are adopted to characterize the phases, morphology, and chemical properties of the as-fabricated catalysts. In contrast to the stacked Bi2WO6, CMS/BWO has numerous exposed edges and open transfer pathways, which can create more open space and reactive sites for photocatalytic reactions. Such favorable characteristics enable CMS/BWO to efficiently degrade organic pollutants (e.g., rhodamine B (RhB), methylene blue (MB), tetracycline hydrochloride (TC)) under visible light. Moreover, the generation of reactive species during the photocatalytic process is also examined by trapping experiments, disclosing the pivotal role of photo-generated holes (h+) and hydroxyl radicals (•OH) in the photo-degradation of pollutants. Above all, this study not only provides an efficient photocatalyst for environmental remediation, but it also opens up new possibilities for waste mussel shell reutilization.

Rare-Earth Metals-Doped Nickel Aluminate Spinels for Photocatalytic Degradation of Organic Pollutants

Visible-light-activated photocatalysts based on samarium-doped, europium-doped, and gadolinium-doped nickel aluminates (SmNA, EuNA, GdNA) were synthesized. The spinel crystalline structures of the doped mixed metal oxides were demonstrated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. The presence of the rare-earth metals (REMs) was confirmed by the energy-dispersive X-ray (EDX) studies. Ultraviolet-visible-near-infrared (UV-Vis-NIR) spectra revealed that the REMs-doped catalysts absorb in the full solar spectrum range covering both visible and near infrared wavelengths. Scanning electron microscopy (SEM) visualized the profound morphological alterations of the doped nickel aluminate samples. Consequently, the pore volume and the Brunauer-Emmett-Teller (BET) surface area decreased, while nanoparticles sizes increased. Fourier-transform infrared spectroscopy (FTIR) exposed that surfaces of REMs-doped nickel aluminates are rich in hydroxyl groups. Finally, the photocatalytic performance was notably increased through doping nickel aluminate (NA) with REMs; the highest activity was observed for EuNA.

Spectroscopic investigation on photocatalytic degradation of methyl orange using Fe2O3/WO3/FeWO4 nanomaterials

In this study, iron oxide (Fe₂O₃), tungsten oxide (WO₃) and iron-tungstate oxide (FeWO₄) nanoparticles (NPs) were synthesized by simple precipitation, acid precipitation, and hydrothermal method respectively. All the spectroscopic analysis reveals that as-synthesized NPs are crystalline with a z-average size of 342, 313 and 373 d.nm respectively. The element compositions, shape and size of the NPs were identified with the help of SEM with EDX analysis. FTIR analysis concluded that the presence of functional groups on the surface of NPs and which responsible for capping and formation of NPs. Besides, the as-synthesized NPs have been used as a photocatalyst for the degradation of Methyl Orange (MO) dye under visible irradiation. FeWO₄ NPs (98%) show more effective in the degradation of MO as compared to other NPs. Moreover, the degraded MO and its by-products were used to assess their toxicity on Vigna radiata and RAW 264.7 cell line and which were confirmed that degraded by-products were non-hazardous.

Enhanced photocatalytic degradation of methyl orange dye on interaction with synthesized ligand free CdS nanocrystals under visible light illumination

Methyl orange is widely used dye in textile industry and later, it becomes the major component of industrial waste and pollutes different water body. So, its degradation is required especially in the case of drinking water. Here, chemically synthesized ligand free CdS nanocrystals have been utilized as a photocatalyst to degrade this dye in water. The mean size of the CdS nanocrystal has been found to be 7 nm approximately from TEM analysis, and SAED pattern shows that these are crystalline in nature. Further, the XRD patterns confirms the cubic structure of CdS nanoparticles and mean size calculated from XRD analysis matches well with the obtained size from TEM study. NMR study clearly verifies that CdS nanocrystals are ligand free stable nanoparticles. Due to this absence of ligand on the surface of CdS nanocrystals, a much enhanced MO degradation has been observed, as the e^--h⁺ pair in the CdS and subsequent generation of free radicals such as hydroxyl, can efficiently oxidize the organic material MO and therefore, degrade this pollutant faster under visible light illumination. The degradation efficiency is found to be 95% after 300 min of illumination, which is much better than the other similar reports.

Superior Adsorption and Photocatalytic Degradation Capability of Mesoporous LaFeO3/g-C3N4 for Removal of Oxytetracycline

Mesoporous LaFeO3/g-C3N4 Z-scheme heterojunctions (LFC) were synthesized via the incorporation of LaFeO3 nanoparticles and porous g-C3N4 ultrathin nanosheets. The as prepared LFC were characterized by transmission electron microscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, powder X-ray diffraction, Raman spectra and N2 adsorption analysis. The structural analysis indicated that the reheating process and the addition of NH4Cl in the thermal polymerization were the key factors to get porous g-C3N4 ultrathin nanosheets and to obtain high specific surface areas of LFC. It remarkably enhanced the adsorption capacity and photocatalytic degradation of LFC for removal of oxytetracycline (OTC). The effect of the mass percentage of LaFeO3 in LFC, pH and temperature on the OTC adsorption was investigated. The LaFeO3/g-C3N4 heterojunction with 2 wt % LaFeO3 (2-LFC) exhibited highest saturated adsorption capacity (101.67 mg g−1) and largest photocatalytic degradation rate constant (1.35 L g−1 min−1), which was about 9 and 5 times higher than that of bulk g-C3N4 (CN), respectively. This work provided a facile method to prepare mesoporous LaFeO3/g-C3N4 heterojunctions with especially well adsorption and photocatalytic activities for OTC, which can facilitate its practical applications in pollution control.

The Improvement of Coralline-Like ZnGa2O4 by Cocatalysts for the Photocatalytic Degradation of Rhodamine B

To date, various methods have been used to synthesize ZnGa2O4 material to promote photodegradation performance. However, cocatalysts, which usually play a crucial role in the photocatalyst system, have not been studied extensively in photocatalytic degradation reactions. In this paper, ZnGa2O4 semiconducting material was synthesized by a traditional high-temperature solid-state reaction. The as-prepared powder was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet–visible diffused reflectance spectroscopy. The results indicate that the as-prepared sample is a highly crystallized granular sample with a bandgap of 4.44 eV and a uniform particle size distribution. Density functional theory (DFT) was utilized to calculate the electronic structure of ZnGa2O4. The valence bands and conduction bands were chiefly composed of O 2p atomic orbitals and the hybridization orbitals of Ga 4s4p and Zn4s4p, respectively. The photocatalytic performance was tested via the decomposition of rhodamine B (RhB) under the irradiation of ultraviolet light. Cu, Ag, Au, Ni, Pt, and Pd cocatalysts were loaded on the ZnGa2O4 photocatalyst by a photodeposition method. The relatively optimal cocatalyst of ZnGa2O4 in the photocatalytic degradation reaction is Au. Thereafter, the effect of loading different usage amounts of the Au cocatalyst for the photodegradation of the ZnGa2O4 photocatalyst was studied in detail. The experimental results displayed that the optimum photodegradation activity was confirmed with the 3 wt% Au/ZnGa2O4 sample, which was 14.1 times more than the unloaded photocatalyst. The maximum photocatalytic degradation ratio of RhB was 96.7%, with 180 min under ultraviolet light.

A Novel Flower-Like Ag/AgCl/BiOCOOH Ternary Heterojunction Photocatalyst: Facile Construction and Its Superior Photocatalytic Performance for the Removal of Toxic Pollutants

Novel 3D flower-like Ag/AgCl/BiOCOOH ternary heterojunction photocatalysts were fabricated by the solvothermal and in-situ precipitation methods, followed by light reduction treatment. The Ag/AgCl nanoparticles were homogeneously distributed on 3D BiOCOOH microspheres. These obtained catalysts were characterized by XRD, SEM, TEM, diffuse reflectance spectra (DRS), and photoluminescence (PL). As expected, they exhibited extraordinary photocatalytic capabilities for the elimination of rhodamine B (RhB) and ciprofloxacin (CIP) under simulated sunlight, the results revealed that the Ag/AgCl/BiOCH-3 with 20 wt.% of Ag/AgCl possessed the maximum activity, and the rate constant for the RhB degradation reached up to 0.1353 min⁻¹, which was about 16.5 or 12.2 times that of bare BiOCOOH or Ag/AgCl. The PL characterization further verified that Ag/AgCl/BiOCOOH heterojunctions were endowed with the effective separation of photogenerated carriers. The excellent photocatalytic ability of Ag/AgCl/BiOCOOH could be credited to the synergistic interactions between Ag/AgCl and BiOCOOH, which not only substantially widened the light absorption, but also evidently hindered the charge recombination. The trapping experiments revealed that the dominant reactive species in RhB removal were h⁺, •OH, and •O₂⁻ species. In addition, Ag/AgCl/BiOCOOH was quite stable and easily recyclable after multiple cycles. The above results imply that the 3D flower-like Ag/AgCl/BiOCOOH ternary heterojunction photocatalyst holds promising prospects in treating industrial wastewater.

Removal of Organic Pollution in the Water Environment

The development of civilization entails a growing demand for consumer goods. A side effect of the production and use of these materials is the production of solid waste and wastewater. Municipal and industrial wastewater usually contain a large amount of various organic compounds and are the main source of pollution of the aquatic environment with these substances. Therefore, the search for effective methods of wastewater and other polluted water treatment is an important element of caring for the natural environment. This Special Issue contains nine peer-review articles presenting research on the determination and removal of environmentally hazardous organic compounds from aqueous samples. The presented articles were categorized into three major fields: new approaches to the degradation of water pollutants, new methods of isolation and determination of the emerging organic contaminants (EOCs), and the occurrence of EOCs in the water environment. These articles present only selected issues from a very wide area, which is the removal of organic pollution in water environment, but can serve as important references for future studies.

High Photocatalytic Activity under Visible Light for a New Morphology of Bi2WO6 Microcrystals

In this work, a new morphology was obtained for bismuth tungstate (Bi2WO6-glyc) using a hydrothermal method with the addition of glycerol as a surfactant. In order to compare, the bismuth tungstate without glycerol as the surfactant, i.e., Bi2WO6, was synthesized. Structural characterization by XRD and Rietveld refinement confirmed the orthorhombic structure as a single phase for all samples with high crystallinity. All active modes in Raman spectroscopy for the orthorhombic phase of bismuth tungstate were confirmed in agreement with XRD analysis. N2 adsorption/desorption and size pore distribution confirmed the high surface area (85.7 m2/g) for Bi2WO6-glyc when compared with Bi2WO6 (8.5 m2/g). The optical band gap by diffuse reflectance was 2.78 eV and 2.88 eV for Bi2WO6-glyc and Bi2WO6, respectively. SEM images confirmed the different morphology for these materials, and microstructures with cheese crisp were observed for Bi2WO6-glyc (cheese crisp). On the other hand, flower-like microcrystals were confirmed for Bi2WO6 sample. The photocatalytic performance of Bi2WO6-glyc (94.2%) in the photodegradation of rhodamine B (RhB) dye solutions at 60 min was more expressive than Bi2WO6 (81.3%) and photolysis (8.2%) at 90 min.

Recent Advances in Carbonaceous Photocatalysts with Enhanced Photocatalytic Performances: A Mini Review

Photocatalytic processes based on various semiconductors have been widely utilized in different applications, with great potential for use in environmental pollution remediation and sustainable energy generation. However, critical issues, including low light adsorption capability, wide energy bandgap, and unsatisfactory physicochemical stability still seriously limit the practical applications of photocatalysts. As a solution, the introduction of carbonaceous materials with different structures and properties into a photocatalyst system to further increase the activity has attracted much research attention. This mini review surveys the related literatures and highlights recent progress in the development of carbonaceous photocatalysts, which include various metal semiconductors with activated carbon, carbon dots, carbon nanotubes/nanofibers, graphene, fullerene, and carbon sponges/aerogels. Moreover, graphitic carbon nitride is also discussed as a carbon-rich and metal-free photocatalyst. The recently developed synthesis strategies and proposed mechanisms underlying the photocatalytic activity enhancement for different applications are summarized and discussed. Finally, ongoing challenges and the developmental direction for carbonaceous photocatalysts are proposed.