Biomass waste from grapefruit peel extract was used for the preparation of MgO–SiO ₂ composites in situ in order to develop effective electrocatalytic composites based on NiO/MgO–SiO ₂ .

The development of low-cost, eco-friendly, and earth-friendly electrode materials for energy storage and conversion applications is a highly desirable but challenging task for strengthening the existing renewable energy systems. As part of this study, orange peel extract was utilized to synthesize a magnesium oxide-silicon dioxide hybrid substrate system (MgO–SiO₂) for coating cobalt oxide nanostructures (Co₃O₄) via hydrothermal methods. A variety of MgO–SiO₂ compositions were used to produce Co₃O₄ nanostructures. The purpose of using MgO–SiO₂ substrates was to increase the porosity of the final hybrid material and enhance its compatibility with the electrode material. This study investigated the morphology, chemical composition, optical properties, and functional group properties. In hybrid materials, the shape structure is inherited from nanoparticles with uniform size distributions that are well compacted. A relative decrease in the optical band was observed for Co₃O₄ when deposited onto an MgO–SiO₂ substrate. An improvement in the electrochemical properties of Co₃O₄/MgO–SiO₂ composites was observed during the measurements of supercapacitors and oxygen evolution reaction (OER) in alkaline solutions. The Co₃O₄/MgO–SiO₂ composite prepared on 0.4 g of the MgO–SiO₂ substrate (sample 2) demonstrated excellent specific capacitance, high energy density, and recycling stability for 40 000 galvanic charge–discharge cycles. The assembled asymmetric supercapacitor (ASC) device demonstrated a specific capacitance of 243.94 F g⁻¹ at a current density of 2 A g⁻¹. Co₃O₄/MgO–SiO₂ composites were found to be highly active towards the OER in 1 M KOH aqueous solution with an overpotential of 340 mV at 10 mA cm⁻² and a Tafel slope of 88 mV dc⁻¹. It was found that the stability and durability were highly satisfactory. Based on the use of orange peel extract, a roadmap was developed for the synthesis of porous hybrid substrates for the development of efficient electrode materials for energy storage and conversion.

In this study, we synthesized hybrid systems based on manganese oxide@zinc oxide (Mn₃O₄@ZnO), using sol gel and hydrothermal methods. The hybrid materials exhibited hierarchical morphologies and structures characterized by the hexagonal phase of ZnO and the tetragonal phase of Mn₃O₄. The hybrid materials were tested for degradation of methylene blue (MB), methyl orange (MO), and malachite green (MG) under ultraviolet (UV) light illumination. The aim of this work was to observe the effect of various amounts of Mn₃O₄ in enhancing the photocatalytic properties of ZnO-based hybrid structures towards the degradation of MB, MO and MG. The ZnO photocatalyst showed better performance with an increasing amount of Mn₃O₄, and the degradation efficiency for the hybrid material containing the maximum amount of Mn₃O₄ was found to be 94.59%, 89.99%, and 97.40% for MB, MO and MG, respectively. The improvement in the performance of hybrid materials can be attributed to the high charge separation rate of electron-hole pairs, the co-catalytic role, the large number of catalytic sites, and the synergy for the production of high quantities of oxidizing radicals. The performance obtained from the various Mn₃O₄@ZnO hybrid materials suggest that Mn₃O₄ can be considered an effective co-catalyst for a wide range of photocatalytic materials such as titanium dioxide, tin oxide, and carbon-based materials, in developing practical hybrid photocatalysts for the degradation of dyes and for wastewater treatment.

The present study describes the use of a leaf extract from Ficus carica as a source of natural antioxidants for the surface alteration of bulk titanium dioxide (TiO₂) in two steps. First, the hydro-thermal treatment of the bulk TiO₂ material was carried out and followed by thermal annealing at 300 °C for 3 h in air. The role of the leaf extract of Ficus carica on the performance of the bulk TiO₂ material for the removal of methylene blue (MB) was also studied. Various analytical techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to explore the crystalline structure, morphology, and composition. The bulk TiO₂ material after the leaf-extract treatment exhibited mixed anatase and rutile phases, a flower-like morphology, and Ti, O, and C were its main elements. The average crystallite size was also calculated, and the obtained values for the bulk TiO₂ material, 18.11 nm, and the treated bulk TiO₂ material with various amounts, 5, 10, and 15 mL, of leaf extract were 16.4, 13.16, and 10.29 nm respectively. Moreover, Fourier-transform infrared spectroscopy validated the typical metal–oxygen bonds and strengthened the XRD results. The bulk TiO₂ material chemically treated with Ficus carica has shown outstanding activity towards the degradation of MB under sunlight. The 15 mL of Ficus carica extract significantly enhanced the photocatalytic activity of the bulk TiO₂ material towards the degradation of MB. The dye degradation efficiency was found to be 98.8%, which was experimentally proven by the Fourier Transform Infrared spectroscopoyy (FTIR) analysis. The obtained performance of the bulk TiO₂ material with Ficus carica revealed excellent surface modifying properties for poorly-performing photocatalysts towards the degradation of synthetic dyes when used in their pristine form. The presented approach suggests that Ficus carica could be of great interest for tuning the surface properties of materials, either in the form of nano-size or bulk-phase in a particular application.

In this study, chloride (Cl⁻) ions were successfully doped into ZnO nanostructures by the solvothermal method. The effect of various Cl⁻ concentrations on the photocatalytic activity of ZnO towards the photodegradation of methylene blue (MB) under the illumination of ultraviolet light was studied. The as-prepared Cl⁻-doped ZnO nanostructures were analyzed in terms of morphology, structure, composition and optical properties. XRD data revealed an average crystallite size of 23 nm, and the XRD patterns were assigned to the wurtzite structure of ZnO even after doping with Cl⁻. Importantly, the optical band gap of various Cl ion-doped ZnO nanostructures was successively reduced from 3.42 to 3.16 eV. The photodegradation efficiency of various Cl⁻ ion-doped ZnO nanostructures was studied for MB in aqueous solution, and the relative performance of each Cl ion-doped ZnO sample was as follows: 20% Cl⁻-doped ZnO > 15% Cl⁻-doped ZnO > 10% Cl⁻-doped ZnO > 5% Cl⁻-doped ZnO > pristine ZnO. Furthermore, the correlation of the pH of the MB solution and each Cl ion dopant concentration was also investigated. The combined results of varying dopant levels and the effect of the pH of the MB solution on the photodegradation process verified the crucial role of Cl⁻ ions in activating the degradation kinetics of MB. Therefore, these newly developed photocatalysts could be considered as alternative materials for practical applications such as wastewater treatment.

Wastewater from the textile industry is chronic and hazardous for the human body due to the presence of a variety of organic dyes; therefore, its complete treatment requires efficient, simple, and low cost technology. For this purpose, we grew ZnO microstructures in the presence of psyllium husk, and the role of psyllium husk was to modify the surface of the ZnO microstructures, create defects in the semiconducting crystal structures, and to alter the morphology of the nanostructured material. The growth process involved a hydrothermal method followed by calcination in air. Additionally, the psyllium husk, after thermal combustion, added a certain value of carbon into the ZnO nanomaterial, consequently enhancing the photocatalytic activity towards the degradation of methylene blue. We also investigated the effect of varying doses of photocatalyst on the photocatalytic properties towards the photodegradation of methylene blue in aqueous solution under the illumination of ultraviolet light. The structure and morphology of the prepared ZnO microstructures were explored by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) techniques. The degradation of methylene blue was monitored under the irradiation of ultraviolet light and in the dark. Also, the degradation of methylene blue was measured with and without photocatalyst. The photodegradation of methylene blue is highly increased using the ZnO sample prepared with psyllium husk. The photodegradation efficiency is found to be approximately 99.35% for this sample. The outperforming functionality of psyllium-husk-assisted ZnO sample is attributed to large surface area of carbon material from the psyllium husk and the synergetic effect between the incorporated carbon and ZnO itself. Based on the performance of the hybrid material, it is safe to say that psyllium husk has high potential for use where surface roughness, morphology alteration, and defects in the crystal structure are vital for the enhancing the functionality of a nanostructured material. The observed performance of ZnO in the presence of psyllium husk provides evidence for the fabrication of a low cost and efficient photocatalyst for the wastewater treatment problems.