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In this work, the physicochemical properties of palm oil fuel ash (POFA) based geopolymers with the addition of graphene oxide (GO) were investigated. Geopolymer composites were prepared by mixing the treated POFA, sand, NaOH, Na2SiO3, and GO. The mixtures were then cast in mortar molds to form the geopolymer composites, with different GO proportions and curing temperatures applied to the composites. Compressive strength, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) analyses, as well as density functional theory (DFT) calculations, have been performed. The compressive test results showed that the compressive strength increased proportionally with the increase of GO content and decreased when there was an excess of GO. The excessive GO and the limited amount of NaOH activator solution inhibited the formation of reduced graphene oxide (rGO) via an in-situ reduction mechanism. The FTIR and SEM analyses revealed that the excess GO tended to promote the formation of epoxy groups on the GO, which eventually confined the formation of dense agglomeration and led to a decrease in compressive strength. The DFT calculations confirmed the significance of the epoxy group stretching. Overall, the ratio of NaOH to GO is a crucial factor in determining the mechanical properties of geopolymers-GO composites.

Nanostructured thin film coatings of copper oxide (Cu-oxide) were investigated to determine their physical structure, surface morphology, surface electronic bonding states, and optical properties. The Cu-oxide had been coated onto reflective aluminum substrates via a facile one-step sol–gel dip-coating route using a copper nitrate precursor. Characterizations were conducted using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), and ultra-violet visible (UV–Vis) spectroscopic methods, and representative sol-gel reactions using copper nitrate precursor were proposed. The XPS spectra confirmed the presence of copper oxide elements. Further exploration of the Cu2p3/2 peak in XPS spectra revealed that the electronic structure of the copper component consisted of tetrahedral Cu(I) and octahedral Cu(II) with the presence of octahedral Cu(II) enabling coatings to have high absorption levels across the solar spectrum. The deconvolution of the O1s spectra exhibited three curve-fitting components: the lattice O2−, surface oxygen, and subsurface O− species. FESEM results showed that the coating surface was an agglomerated copper oxide nanoparticles structure forming a porous structure. The optical band-gap of Cu-oxide thin film coatings, via the Tauc plot, was 2.7 eV.

This article presents a comprehensive study on surface chemical bonding states, morphological features, mechanical properties, finite element modeling, and water contact angle measurements of wet chemical based dip-coated CoZn-oxide thin film coatings. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Nanoindentation, finite element method (FEM) modeling, and drop shape analysis techniques were used to carry out the detailed measurements. AFM studies showed that the surface roughness values of all the coatings sturdily increased with the increase in sol concentrations. The gradual increase in sol concentrations and annealing temperature also had a remarkable influence over the Co , and Zn-contents of these coatings given by XPS analysis. The deconvolution of Co 2p3/2 photoelectron lines revealed the formation of Co(OH)2, CoO, Co2O3, and Co3O4 phases from the coatings surface while low intensity satellite peaks developed due to a partial spinel lattice structure of Co-ions. The occurrence of Co3O4, CoO, and ZnO phases were also confirmed from the deconvolution of O 1s photoelectron lines. The elastic modulus, E, of CoZn-oxide thin film coating, varied within the range of 43.7–69.2 GPa was comparable with that in CoCuO thin film coatings. The maximum stress level induced was estimated to be in the range of 4.0–6.5 GPa. However, as the thickness of the coatings is increased, the maximum stress level slightly decreased. The coatings were moderately hydrophobic.

Ce/Ti mixed metal oxide thin films have well known optoelectrical properties amongst several other physio-chemical properties. Changes in the structural and mechanical properties of magnetron sputtered Ce/Ti oxide thin films on Si (100) wafers with different Ce:Ti ratios are investigated experimentally and by modelling. X-ray Photoemission Spectroscopy (XPS) and X-ray diffraction (XRD) confirm the primary phases as trigonal Ce2O3 and rutile form of TiO2 with SiO2 present in all prepared materials. FESEM imaging delivers information based on the variation of grain size, the mixed Ce/Ti oxides providing much smaller grain sizes in the thin film/substrate composite. Nanoindentation analysis concludes that the pure cerium oxide film has the highest hardness value (20.1 GPa), while the addition of excess titanium oxide decreases the hardness of the film coatings. High temperature in-situ XRD (up to 1000 degrees C) results indicate high thermal phase stability for all materials studied. The film with Ce:Ti = 68%:32% has a new additional minor oxide phase above 800 degrees C. Contact angle experiments suggest that the chemical composition of the surface is insignificant affecting the water contact angle. Results show a narrow band of 87.7-95.7 degrees contact angle. The finite element modelling (FEM) modelling of Ce/Ti thin film coatings based on Si(100); Si(110); silica and steel substrates shows a variation in stress concentration.

The influence of the reaction gas composition during the DC magnetron sputtering process on the structural, chemical and optical properties of Ce-oxide thin films was investigated. X-ray diffraction (XRD) studies confirmed that all thin films exhibited a polycrystalline character with cubic fluorite structure for cerium dioxide. X-ray photoelectron spectroscopy (XPS) analyses revealed that cerium is present in two oxidation states, namely as CeO2 and Ce2O3, at the surface of the films prepared at argon-oxygen flow ratios between 0–7%, whereas the films are completely oxidized into CeO2 as the aforementioned ratio increases beyond 14%. Various optical parameters for the thin films (including an optical band gap in the range of 2.25 – 3.1 eV) were derived from the UV-Vis reflectance. A significant change in the band gap was observed as the oxygen pressure was raised from 7% to 14% and this finding is consistent with the high-resolution XPS analysis of Ce 3d that reports a mixture of Ce2O3 and CeO2 in the films. Density functional theory (DFT+U) implemented in the Cambridge Serial Total Energy Package (CASTEP) was carried out to simulate the optical constants of CeO2 clusters at ground state. The computed electronic density of states (DOSs) of the optimized unit cell of CeO2 yields a band gap that agrees well with the experimentally measured optical band gap. The simulated and measured absorption coefficient (α) exhibited a similar trend and, to some extent, have similar values in the wavelength range from 100 to 2500 nm. The combined results of this study demonstrate good correlation between the theoretical and experimental findings.

The copper and cobalt oxides composites coatings on aluminum substrates have been successfully synthesized via sol-gel method using nitrate-based sol precursors. The composites were characterized by X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), and UV-Vis-NIR spectrophotometry. The sol-gel reactions were discussed and Molecular Dynamics (MD) simulation was integrated into the study to predict molecules assembly properties. The XRD analyses revealed that the CuO and the Co3O4 composites were formed after the annealing process with the average difference of the calculated lattice parameters compared to ICDDs was 1.17%. The surface electronic structure was mainly consisted of tetrahedral Cu(I), octahedral Cu(II), tetrahedral Co(II), octahedral Co(III) as well as surface, sub-surface and lattice oxygen O−. The XRD, XPS and MD simulation results showed that there was minimal (or possibly non-existing) indication of copper-cobalt mixed phase oxides formations. FESEM and AFM surveys revealed that the coating had a porous surface composed of interlinked nanoparticles in the range of ~10 to ~40 nm. UV-Vis-NIR reflectance spectra showed that the sol precursors concentration and the dip-drying cycle significantly influenced the absorptance value with optimum absorptance (α) of 88.7% exhibited by coating synthesized using sol concentration of 0.1 M and 10 dip-drying cycles. High absorptance value and simplicity in the synthesis process render the coatings to be very promising candidates for solar selective absorber (SSA) applications.

Copper cobalt oxide (Cu2CoO3) thin film coatings integrated with silica (SiO2) antireflection (AR) layer have been deposited on the top of aluminum substrates using a simple sol-gel dip-coating method. Reflectance spectra of the coatings were generated using spectroscopic methods while the coatings were subjected to an accelerated thermal durability test. The addition of silica changed the reflectance spectra of coatings within the wavelength range of 0.3–15.4 µm. The absorptance decreased with the increase of the withdrawal rate in range of 10–40 mm/min, while the emittance increased with the increase of the withdrawal rate. The optimum optical parameters for this study were absorptance, αS=84.96%; emittance, eT=5.63% corresponding to the coating with a silica AR layer at withdrawal rate of 10 mm/min. The coatings with the silica AR layer were shown to be thermally durable in which no discernible ‘cracking’ phenomenon was observed. The degradation of the coatings with the silica AR layer was predominantly governed by temperature changes rather than exposure time.

Potassium manganese oxide (KMn8O16) nanowires were synthesized using a customized hydrothermal method and characterized using scanning-electron microscopy, X-ray diffractometry and thermogravimetric analysis to determine the effects of reaction temperatures and molar ratio of reactants on the crystallinity and morphology of the synthesized nanowires. It was established that increasing the stoichiometric portion of potassium precursors increased the average nanowire diameter though such effect was comparatively less prominent in terms of reaction temperature. Deficient supply of potassium inhibited nanowires growth in which only KMn8O16 (cryptomelane) growth orientations of (211), (301) and (600) were observed along with traces of MnO2, resulting in a wool-like nanowires suspension.