Synergistic cobalt oxide/reduced graphene oxide/biochar nano-composite catalyst: harnessing the power of the catalyst for sustainable remediation of organic dyes and chromium(vi)

The exponential growth of industrial activities has led to a significant rise in the release of organic effluents, containing hazardous heavy metals and dyes, into the environment. These pollutants exhibit resistance to conventional biodegradation processes and are associated with carcinogenic properties, posing a severe threat to living organisms. In this context, the present research endeavours to address this environmental challenge through the development of an affordable and efficient photocatalyst, the Co3O4/reduced graphene oxide/biochar (CBG-10) heterostructure. The structural analysis of CBG-10, conducted through various techniques such as XRD, XPS, SEM, and optical property measurements, demonstrates its potential as a highly effective and easily recoverable catalyst for the mineralization of persistent pollutants like methylene blue, malachite green, and hexavalent Cr(vi). The recyclability of CBG-10 was confirmed through XRD studies, highlighting its stability and practical usability in wastewater purification. The photocatalytic behaviour of the catalyst was attributed to the generation of hydroxyl (˙OH) and superoxide radicals (˙O2-) during visible light illumination, as revealed by quenching experiments. The cost-effectiveness and stability of CBG-10 position it as a promising solution for addressing the challenges associated with the removal of stubborn organic contaminants from wastewater, thereby contributing to environmental protection and public health.

Waste toner-derived porous iron oxide pigments with enhanced catalytic degradation property

'Wealth from Waste' is an emerging concept, since it leads an effective waste treatment and waste recyclability. On the other hand, cost effective production iron oxide (IO) nanomaterials is still needed to develop, owing to their wide applications. Herein, we proposed a simple direct calcination method to prepare porous IO (Fe₃O₄ and Fe₂O₃) nanomaterials from waste toner powder. Characterization techniques reveal that a structural change happened from Fe₃O₄ to γ-Fe₂O₃ and γ-Fe₂O₃ to α-Fe₂O₃ at the calcination temperature of 500 °C and 700 °C respectively. Consequently, optical (band gap) and magnetic parameters of IO samples were significantly varied. The pigment characteristics of the IO samples were evaluated using Commission Internationale de l'Eclairage (CIE) analysis. IO900 sample has shown good brown-red coloration (L* = 43.11, a* = 13.26 and b* = 5.69) and it also exhibited good stability in acidic and basic conditions. Practical applicability of IO pigments were also tested by mixing with plaster of paris (PP) powder. Further, porous IO samples were also used as catalysts in the reductive degradation of methyl orange (MO) dye in presence of excess sodium borohydride (NaBH₄). IO, prepared at 900 °C exhibited ∼99.9% reduction efficiency within 40 min. Recycling experiments indicated that IO900 possess good stability up to seven cycles. The present porous IO samples will become potential in pigment and environmental remediation.

Synthesis, Characterization and Photodegradation Studies of Copper Oxide–Graphene Nanocomposites

In this work, a simple hydrothermal method was employed to prepare a pristine sample of copper oxide (CuO) and three samples of copper oxide–graphene nanocomposites (CuO-xG) with x = 2.5, 5, and 10 mg of graphene. The synthesized samples were characterized using X-ray powder diffractometry (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR) and ultraviolet–visible (UV-Vis) spectroscopy. The XRD patterns of CuO-xG nanocomposites exhibited the diffraction peaks related to the crystal planes of monoclinic CuO and hexagonal graphite. The surface morphology of the prepared samples was investigated using FESEM images. EDX analysis was used to investigate the chemical composition of the synthesized samples. FTIR spectroscopy identified the vibrational modes of the covalent bonds present in the samples. The allowed direct optical bandgap energy was calculated for all prepared samples using UV-Vis absorption spectra. The small bandgap of CuO-xG nanocomposites indicates their potential use as an effective photocatalyst in the presence of visible light. Photocatalytic activity of the samples was explored for the degradation of methylene blue (MB) dye contaminant under visible light irradiation. The results showed that the CuO-5G sample has the highest photodegradation efficiency (~56%).

Recent progress in green and biopolymer based photocatalysts for the abatement of aquatic pollutants

Enormous research studies on the abatement of anthropogenic aquatic pollutants including organic dyes, pesticides, cosmetics, antibiotics and inorganic species by using varieties of semiconductor photocatalysts have been reported in recent decades. Besides, many of these photocatalysts suffer in real applications owing to their high production cost and low stability. In many cases, the photocatalysts themselves are being considered as secondary pollutants. To eliminate these drawbacks, the green synthesized photocatalysts and the use of biopolymers as photocatalyst supports are considered in recent years. In this context, recent developments in green synthesized metals, metal oxides, other metal compounds, and carbon based photocatalysts in water purification are critically reviewed. Furthermore, the pivotal role of biopolymers including chitin, chitosan, cellulose, natural gum, hydroxyapatite, alginate in photocatalytic removal of aquatic pollutants is comprehensively reviewed. The presence of functional groups, electron trapping ability, biocompatibility, natural occurrence, and low production cost are the major reasons for using biopolymers in photocatalysis. Finally, the summary and conclusion are presented along with existing challenges in this research area.

Challenges and prospects about the graphene role in the design of photoelectrodes for sunlight-driven water splitting

Graphene and its derivatives have emerged as potential materials for several technological applications including sunlight-driven water splitting reactions. This review critically addresses the latest achievements concerning the use of graphene as a player in the design of hybrid-photoelectrodes for photoelectrochemical cells. Insights about the charge carrier dynamics of graphene-based photocatalysts which include metal oxides and non-metal oxide semiconductors are also discussed. The concepts underpinning the continued progress in the field of graphene/photoelectrodes, including different graphene structures, architecture as well as the possible mechanisms for hydrogen and oxygen reactions are also presented. Despite several reports having demonstrated the potential of graphene-based photocatalysts, the achieved performance remains far from the targeted benchmark efficiency for commercial application. This review also highlights the challenges and opportunities related to graphene application in photoelectrochemical cells for future directions in the field.

Role of solution chemistry in the attachment of graphene oxide nanoparticles onto iron oxide minerals with different characteristics

Given the ubiquity and abundance of the iron oxide minerals and their important roles in affecting the environmental fate of graphene oxide (GO) nanoparticles, the attachment of GO onto three iron oxide minerals (i.e., hematite, goethite, and ferrihydrite) under different solution chemistry conditions was investigated in this study. The main mechanism of the attachment of GO was electrostatic interaction. Calculations based on the DLVO theory showed that the attachment was a favorable process. Interestingly, the affinity of GO towards three iron oxide minerals was in the order of ferrihydrite > goethite > hematite. This result indicates that different characteristics of various iron oxides (e.g., specific surface area, crystal structure, and surface charge, and surface hydroxyl densities) can influence their attachment capacities for GO. The attachment of GO depended on the solution pH and ionic strength. Electrostatic attraction and hydrogen bonding were the important retention mechanisms for GO attachment when pH < pH_PZC (the point of zero charge) and pH > pH_PZC, respectively. The attachment capacities of iron oxides decreased with increasing ionic strength at lower pH because of the decrease of the electrostatic attraction. Meanwhile, the presence of divalent cations (i.e., Ca²⁺ and Cu²⁺) could significantly promote GO attachment mainly by the surface-bridging mechanism. Meanwhile, the enhancement effect of Cu²⁺ was greater than Ca²⁺ due to the greater complexation affinity of Cu²⁺. Furthermore, attachment isotherms showed that the presence of phosphate could inhibit the attachment of GO onto minerals obviously. Because phosphate could form inner-sphere surface complex on the iron oxide surface, and consequently decreased the electrostatic attraction between nanoparticles and minerals. Our study has important implications for predicting the fate of GO in natural environment where amounts of iron oxide minerals are present.

Designing vertically aligned porous NiCo2O4@MnMoO4 Core@Shell nanostructures for high-performance asymmetric supercapacitors

NiCo₂O₄@MnMoO₄ core@shell nanostructures are synthesized as electrode material using hydrothermal method for the fabrication of asymmetric supercapacitor (ASC) device. The NiCo₂O₄@MnMoO₄ electrode shows better electrochemical performance with specific capacitance (SC) of 1821 F/g at current density of 5 A/g and cycling stability of 94%. The NiCo₂O₄@MnMoO₄ core@shell electrode shows better SC compared to pure NiCo₂O₄ and MnMoO₄ electrodes. An ASC device is fabricated using NiCo₂O₄@MnMoO₄ as a positive and rGO/Fe₂O₃ as negative electrode materials. Remarkably, the fabricated device shows a SC of 294 F/g at current density 4 A/g, with an energy density of 91.87 Wh/kg at a power density of 374.15 W/kg. The device shows good reversibility with cycling stability of 68% after 2,000 cycles. The ASC device is used to illuminate nine green color LEDs for 35 min. Therefore, the present report provides a simple method to fabricate efficient and stable energy storage devices for industrial applications.

Efficient visible light-driven core–shell-structured ZnS@Ag2S nanoparticles-anchored reduced graphene oxide for the reduction of Cr(vi)

Synthesis of a ZnS@Ag₂S/RGO nanocomposite with high photocatalytic performance for the removal of Cr(vi) based on the photo-induced interfacial charge transfer.

Fabrication of Ag@Co-Al Layered Double Hydroxides Reinforced poly(o-phenylenediamine) Nanohybrid for Efficient Electrochemical Detection of 4-Nitrophenol, 2,4-Dinitrophenol and Uric acid at Nano Molar Level

In this paper, Co-Al layered double hydroxides (LDHs), Co-Al LDHs/poly(o-phenylenediamine) (PoPD) and Ag nanoparticles decorated Co-Al LDHs/PoPD (Ag@Co-Al LDH/PoPD) samples were prepared. The as-prepared samples were characterized by XRD, Raman, XPS, FT-IR, DRS-UV-Vis, PL and TGA techniques. The salient features of morphology and size of the samples were determined using FESEM, and HR-TEM. Then, the samples were coated on glassy carbon electrode (GCE) and employed for sensing of 4-nitrophenol (4-NP), 2,4-dinitrophenol (2,4-DNP)) and uric acid (UA). It was found that Ag@Co-Al LDH/PoPD/GCE showed superior electrochemical sensing behaviour than other modified electrodes. It exhibits the detection limit (DL) of 63 nM, 50 nM and 0.28 µM for 4-NP, 2,4-DNP and UA respectively.

Silver doped reduced graphene oxide as a promising plasmonic photocatalyst for oxidative coupling of benzylamines under visible light irradiation

Visible light assisted photocatalytic reduction of nitro-compounds has been found as an efficient and sustainable approach for the production of amines.