Solvothermal synthesis has shown to have a great potential to synthesize Zinc Oxide nanoparticles (ZnO NPs) with less than 10 nm size. In this study, we present a rapid synthesis of ZnO NPs in which ZnO NPs with more uniform shape and highly dispersed were synthesized using zinc acetate dihydrate (Zn(CH 3 COO) 2 2H 2 O) and potassium hydroxide (KOH) as a precursor and absolute ethanol as solvent via solvothermal method. Few techniques were exploited to characterize synthesized ZnO NPs including X-ray diffraction (XRD), transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET), energy-dispersive X-ray spectroscopy (EDX), fourier transform infrared (FT-IR) spectroscopy, and ultraviolet visible (UV-Vis) spectroscopy. Synthesized ZnO NPs that were prepared via solvothermal synthesis method at 60 °C for 3 hours exhibited a wurtzite structure with a crystalline size of 10.08 nm and particle size of 7.4 ± 1.2 nm. The UV-vis absorption spectrum has shown peak at 357 nm indicate the presence of ZnO NPs. Hence, better quality with uniform size ZnO NPs can be easily synthesized with reduced amount of time via solvothermal synthesis method rather than using other complicated and lengthy synthesis methods.

Some industrial wastes are shown to be useful in the production of mullite ceramics. These industrial wastes are rich in certain metal oxides such as silica (SiO2) and alumina (Al2O3). This gives wastes the potential to be used as a starting material source for mullite ceramics preparation. The purpose of this review paper is to compile and review various mullite ceramics preparation methods that utilized a variety of industrial wastes as starting materials. This review also describes the sintering temperatures and chemical additives used in the preparation and its effects. A comparison of both mechanical strength and thermal expansion of the reported mullite ceramics prepared from various industrial wastes were also addressed in this work.

Summary Reduced graphene oxide (RGO) has progressed as one of key emerging carbon for catalyst support material. As an alternative to the conventional RGO precursor, biomass Sengon wood was converted into RGO for use as a noble metal free catalyst support in oxygen reduction reaction (ORR). This work intends to reveal the applicability of Sengon wood‐derived RGO in anchoring/doping iron and nitrogen particles onto its surface and to study its ORR performance in a half‐cell environment. Thin‐sheet layer and highly defective (ID/IG) was gradually obtained at elevated pyrolysis temperature of Sengon wood graphene oxide (GO) at range 700°C to 900°C. As prepared RGO was further doped into catalyst (Fe/N/RGO) through the same pyrolysis procedure at a selected temperature after mixing the GO powder with iron chloride and different nitrogen precursors (urea, choline chloride, and polyaniline) at a fixed ratio. The ORR activity reached a current density up to 2.43 mA/cm2, which in conjunction with smooth multilayer sheet morphology and high graphitic‐N content as the active sites. Stability analysis indicated an 85% current efficiency and only 0.03 V reduction in onset potential on methanol resistant test for Fe/ChoCl/RGO catalyst. This study revealed that Sengon wood‐derived RGO successfully supported Fe‐N‐C catalyst which showed comparable oxygen reduction activity to Pt/C.

Porous mullite ceramics were produced using mullite precursor and modified cenospheres as a non-sacrificial pore-forming agent. The cenospheres used are aluminosilicate hollow spheres with high silica and alumina content, which are obtained from coal-fired power plant. In this study, the cenospheres were modified using aluminum trichloride hexahydrate (AlCl3•6H2O), alkali/acid leaching and heat treatment. Various types and amounts of the modified cenospheres were mixed with mullite precursor to produce porous mullite ceramics for subsequent firing at 1500 °C. Graphite powder, as sacrificial pore-forming agent, was also used to prepare porous mullite ceramics by the same processing conditions for comparison. The study found that the use of graphite powder was unable to increase the porosity of the mullite ceramics as a result of excessive shrinkage. It acted more as a sintering aid rather than as sacrificial pore-forming agent. On the other hand, addition of modified cenospheres as non-sacrificial pore-forming agent leads to the increment of both total porosity and closed porosity, with the reduction of open porosity. The results showed that with the addition of 40 wt% of modified cenospheres to the mullite precursor, the resultant porous mullite ceramic has a total porosity of 50.2%, thermal conductivity of 1.28 Wm−1K−1, linear shrinkage of 4%, and biaxial flexural strength of 45.9 MPa. Porous mullite ceramic with majority closed pores has potential application for high temperature thermal barrier.

We report, for the first time, a facile, scalable, and costeffective method for the synthesis of high-performance and monodispersed hexagonally shaped cobalt oxide platelets supported on iron oxides (Fe 3 O 4 and α-Fe 2 O 3 ) as the electrocatalyst systems for water electrolysis. The Fe 3 O 4 was synthesized in the absence of an inert environment and organic solvent, using a modified coprecipitation procedure. Fe 3 O 4 nanoparticles of average size 15 nm served as the best catalyst support for Co 3 O 4 , in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). A current density of 10 mA/cm 2 was achieved, at −0.36 and 1.64 V for the HER and OER [versus reversible hydrogen electrode (RHE)], respectively, for the Co 3 O 4 /Fe 3 O 4 system, in 0.1 M KOH with low total catalyst loading of 250 μg/cm 2 (or 100 μg Co 3 O 4 /cm 2 ). Compared to those using the same total loading of unsupported Co 3 O 4 catalyst, the overpotentials of Co 3 O 4 / Fe 3 O 4 catalyst decreased by 0.22 and 0.06 V for the HER and OER, respectively. Despite low nonprecious metal loading, the Co 3 O 4 /Fe 3 O 4 system showed high OER kinetics with low Tafel slope of 63 mV/dec. Chronoamperometry tests performed, at 1.62 and −0.30 V for the OER and HER, respectively, on the Co 3 O 4 /Fe 3 O 4 catalyst demonstrated extremely stable OER over a period of 8 h. FESEM images of Co 3 O 4 /Fe 3 O 4 revealed that the Co 3 O 4 platelets were self-assembled into edge-on orientation on the Fe 3 O 4 support. This largely accounted for the high catalytic activities observed because of the large total exposed surface area of Co 3 O 4 /Fe 3 O 4 for catalytic reactions, in addition to electrochemical and morphological effects. Despite negating the need for specially tailored morphologies, Co 3 O 4 /Fe 3 O 4 demonstrated enhanced electrochemical performance and stability. This may serve as a cost-effective route to the large-scale commercialization of electrolyzers and fuel cells via facile synthesis of nonprecious metal oxides as the catalyst−support system for enhanced electrochemical water electrolysis.

Zinc oxide is an important material with numerous applications due to its unique properties. Due to their thermal and chemical stability are used in wide applications such as LEDs, sensors, catalysts, and photodetectors. Different chemical, physical, and biological methods have been adopted to achieve the intended result, as enumerated in many pieces of literature. Therefore, selecting an efficient synthesis process is essential, which is a key factor that significantly influences the efficacy of the synthesized nanocrystalline materials. The chemical synthesis of nanoparticles (NPs) via hydrothermal, solvothermal, and sol-gel routes is considered effective as high-quality crystalline structures are produced. Control of parameters of processes yields excellent morphological features of the synthesized samples. This review explored the different parameters of processes and their effect on the morphology of ZnO nanostructures via hydrothermal, solvothermal, and sol-gel techniques. Finally, some ZnO nanocomposites molecules are reviewed as per the dopant used and its effect on the sample compound synthesized.

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ZnO nanofibers were successfully prepared by electrospinning a precursor mixture of polyvinylpyrrolidone (PVP)/zinc acetate, followed by calcination treatment of the electrospun composite nanofibers. The effect of applied voltage to the morphology of nanofibers was studied. Both PVP/Zn acetate and ZnO nanofibers were characterized by FESEM and XRD. The results show that the diameter of the nanofibers changed with applied voltage. Results found that the optimum calcined temperature was 500°C to produce continuous ZnO nanofibers.