In the present work, PbO-x wt% Al₂O₃ nanocomposites (where x = 0, 10, 20, 30, 40, 50, 60, 70, and 100 wt%) were prepared by a microwave irradiation method. Their structural parameters, morphology, and chemical bonds, were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR). It was noticed that the produced phases have an orthorhombic crystal structure and the smaller average crystallite sizes were formed when the ratio of Al₂O₃ is 40 wt%. The FTIR analysis reveals the formation of various bonds between Al or Pb and O. The TEM analysis reveals that the PbO-x%Al₂O₃ composites (x = 20, 40, and 60), composed of dense particles, and their size are smaller compared to the pure Al₂O₃ sample. The optical bandgap obeys the direct allowed transition and decreases from 4.83 eV to 4.35 eV as the PbO ratio in the composites increases from 0 to 100%. The intensity of the photoluminescence emission, at the same wavelength, increases as the PbO ratio increases from 0% to 60% implying that increasing the PbO content increases the capacity of free carriers within the trap centers. The prepared composites are used as a catalyst to remove the methylene blue (MB) from the wasted water under UV-visible or visible light irradiations. The photocatalytic degradation of MB was investigated by applying various kinetic models. It was found that the PbO-30% Al₂O₃, and PbO-40% Al₂O₃ composites are the best ones amongst other compositions. Furthermore, the pseudo-second-order model is the best model for describing the deterioration mechanism among the models studied. The formed composites could be suitable for the degradation of organic dyes for water purification as well as applications that required a higher optical bandgap.

Novel materials with nanostructures are effective in controlling the physical properties needed for specific applications. The use of active and sensing materials is increasing in many applications, such as gas sensing. In the present work, we attempted to synthesize incorporated Cu²⁺ into the SnO₂ matrix as Cu_xSn_1−xO₂ nanocomposite using a cost-effective precursor and method. It was observed that, at low concentrations of copper precursor, only SnO₂ phase could be detected by X-ray diffraction (XRD)_. The distribution of Cu in the SnO₂ matrix was further measured by elemental analysis of energy-dispersive X-ray (EDX) mapping and X-ray fluorescence (XRF). At high copper concentration, a separated monoclinic phase of CuO was formed (noted here as CuO/SnO₂). The average crystallite size was slightly reduced from 5.9 nm to 4.7 nm with low doping of 0.00–5.00% Cu but increased up to 15.0 nm at high doping of 10.00% Cu upon the formation of separated SnO₂ and CuO phases. The formation of Cu–SnO₂ or CuO phases at low and high concentrations was also observed by photoluminescent spectra. Here, only the emission peak of SnO₂ with a slight blueshift was recorded at low concentrations, while only the CuO emission peak was recorded at high concentration. The effect of Cu concentration on the sensing properties of SnO₂ toward methane (CH₄) gas was also investigated. It was found that the sensor embedded with 2.00% Cu exhibited an excellent sensitivity of 69.0 at 350 °C and a short response–recovery time compared with the other sensors reported here. The sensing mechanism of Cu_xSn_1−xO₂ and CuO/SnO₂ is thus proposed based on Cu incorporation.

In order to improve the sensitivity and to reduce the working temperature of the CH₄ gas sensor, a novel 1D nanostructure of CuO-doped In₂O₃ was synthesized by the co-evaporation of Cu and In granules. The samples were prepared with changing the weight ratio between Cu and In. Morphology, structure, and gas sensing properties of the prepared films were characterized. The planned operating temperatures for the fabricated sensors are 50–200 °C, where the ability to detect CH₄ at low temperatures is rarely reported. For low Cu content, the fabricated sensors based on CuO-doped In₂O₃ showed very good sensing performance at low operating temperatures. The detection of CH₄ at these low temperatures exhibits the potential of the present sensors compared to the reported in the literature. The fabricated sensors showed also good reversibility toward the CH₄ gas. However, the sensor fabricated of CuO-mixed In₂O₃ with a ratio of 1:1 did not show any response toward CH₄. In other words, the mixed-phase of p- and n-type of CuO and In₂O₃ materials with a ratio of 1:1 is not recommended for fabricating sensors for reducing gas, such as CH₄. The gas sensing mechanism was described in terms of the incorporation of Cu in the In₂O₃ matrix and the formation of CuO and In₂O₃ phases.

In this paper, we have reported a low-concentration active electrolyte of KBrO₃ for the supercapacitor’s application. The electrochemical processes were carried out in two concentrations of KBrO₃ with 0.2 and 0.4 M. Additionally, we have reported a novel strategy for doping graphene during its fabrication process with a potassium bromide (KBr) solution. The chemical doping of graphene with KBr improved the electrochemical properties of graphene used as supercapacitors. HRTEM images confirmed the multi-layer graphene obtained by CO₂ laser based on polyimide. The effect of KBr on the graphene lattice has been studied using Raman spectroscopy. The two electrodes of graphene and KBr-doped graphene were subjected to the electrochemical properties study as a supercapacitor by electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge techniques. The results exhibited the successful method of graphene doping and the stability of using KBrO₃ as a suitable electrolyte for electrochemical processes with this lower molarity. The specific capacitance of the pristine graphene capacitor in 0.2 M of KBrO₃ was 33 Fg⁻¹, while this value increased up to 70 Fg⁻¹ for KBr-doped graphene in 0.4 M of KBrO₃. The specific capacity in mAhg⁻¹ has also increased twofold. The results exhibited the possibility of using KBrO₃ as an electrolyte. The supercapacitor performance almost showed good stability in the life cycle.

The quantum size of materials is an effective property for specific physical applications. The theoretical approach helps in understanding the physical properties of these materials. SnO₂ quantum crystals of ~ 1.8–6.0 nm are prepared by a hydrothermal method. The size of crystals is smaller than the Debye length reported for SnO₂ at 250 °C. The emission spectra of the radiative recombination between conduction and valence bands show a blue shift, which confirms the electron confinement. The prepared materials are used for fabricating gas sensor tested for CH₄ gas. The gas detecting measurements exhibited high sensitive quantum crystals, QCs, toward CH₄. For the first time, a theoretical approach is formulated for the response of SnO₂ toward CH₄ to understand the sensing mechanism of the quantum crystals. The correlation between the theoretical and experimental results clarified the reason of the high response observed for the quantum crystals toward CH₄. To conduct a high response, the crystal size should be comparable or less than the Debye length, which means that the crystal is fully depleted or in volume-depleted in the air. Thus, the high response obtained here is explained in terms of the proposed theoritical approach.