Optical properties of hydrothermally synthesised and thermally annealed ZnO/ZnO2 composites

Optimization and kinetic analysis of electrocoagulation-assisted adsorption for treatment of young landfill leachate

An investigation was conducted on the electrocoagulation treatment of high-strength young landfill leachate using an electrode made of aluminium in a batch electrochemical cell reactor. An iron sheet of 1 m⨯1 m⨯1.1 m (L: B: H) was used to construct the two landfill simulating reactors, both the reactors were operated at different conditions, i.e., one without rainfall (S1) and the other with rainfall (S2). Both reactors have 51% wet and 49% dry waste, which is the typical waste composition of India, and the quantity of waste taken was 450 kg; hence, the generated leachate was treated. This work focuses on the utilization of electrocoagulation as the sole treatment method where coagulation and adsorption occur simultaneously for young landfill leachate. The study employed a central composite design (CCD) to systematically vary the initial pH, current density (CD), and reaction time to examine their impact on the removal efficiency of COD (Chemical oxygen demand), TOC (Total organic carbon), and TSS (Total Suspended Solids). The optimum conditions obtained were a pH of 7.35, a CD of 15.29 mA/cm2, and a reaction duration of 57 min. When the conditions were optimized, the COD, TSS, and TOC removal efficiencies were 83.56%, 73.12%, and 85.58%, respectively. Also, the electrodes depleted 2.78 g of Al/L. In addition, pseudo-first-order and pseudo-second-order kinetics were employed to examine the elimination of contaminants by adsorption on aluminium hydroxide, thereby confirming the adsorption process. After investigation through energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD), with the produced sludge confirmed that electrocoagulation removed a significant amount of metals from landfill leachate.

A comprehensive correlated analysis of Ra-Doped (ZnO2, ZnO) for optoelectronic applications: a first-principle study

CONTEXT

Zinc oxide (ZnO) exhibits bulk-like behavior and is modified by radium doping to attain favorable electronic properties. The elastic and mechanical response of ZnO₂ is much more favorable than ZnO material. The change in thermal expansion, Debye temperature, free energy, entropy, and specific heat leads it to be a good candidate for thermodynamic applications at low and high temperatures. Optical properties like dielectric function, absorption, refraction, reflection, and refractive index obtained after suitable doping transform the material as optically active. ZnO₂ has low reflectivity and zero absorption below the electronic band gap as compared to ZnO in a wider spectral range. Our analyses on doped ZnO₂ and ZnO make us confident for a wide range of applications in optoelectronic and anti-bacterial treatment in biomedical devices. Especially due to high flexibility and high light transmission, ZnO₂ is an excellent applicant for transparent electrodes.

METHODS

Density functional theory has been employed in consistency with generalized gradient approximation (GGA) with PBEsol to analyze the structural, electronic, elastic, mechanical, thermodynamic, and optical response of pure and Ra-doped (ZnO₂ and ZnO) materials.

Electrochemical and photoluminescence response of laser-induced graphene/electrodeposited ZnO composites

The inherent scalability, low production cost and mechanical flexibility of laser-induced graphene (LIG) combined with its high electrical conductivity, hierarchical porosity and large surface area are appealing characteristics for many applications. Still, other materials can be combined with LIG to provide added functionalities and enhanced performance. This work exploits the most adequate electrodeposition parameters to produce LIG/ZnO nanocomposites. Low-temperature pulsed electrodeposition allowed the conformal and controlled deposition of ZnO rods deep inside the LIG pores whilst maintaining its inherent porosity, which constitute fundamental advances regarding other methods for LIG/ZnO composite production. Compared to bare LIG, the composites more than doubled electrode capacitance up to 1.41 mF cm-2 in 1 M KCl, while maintaining long-term cycle stability, low ohmic losses and swift electron transfer. The composites also display a luminescence band peaked at the orange/red spectral region, with the main excitation maxima at ~ 3.33 eV matching the expected for the ZnO bandgap at room temperature. A pronounced sub-bandgap tail of states with an onset absorption near 3.07 eV indicates a high amount of defect states, namely surface-related defects. This work shows that these environmentally sustainable multifunctional nanocomposites are valid alternatives for supercapacitors, electrochemical/optical biosensors and photocatalytic/photoelectrochemical devices.

Monitoring the process of formation of ZnO from ZnO2usingin situcombined XRD/XAS technique

Use ofin situcombined x-ray diffraction and x-ray absorption spectroscopy for the study of the thermal decomposition of zinc peroxide to zinc oxide is reported here. Comparison of data extracted from both x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) with thermo gravimetric analysis (TGA) enabled us to follow the nature of the conversion of ZnO₂to ZnO. A temperature range between 230 °C and 350 °C appears to show that a very poorly crystalline ZnO is formed prior to the formation of an ordered ZnO material. Both the decrease in white line intensity in the Zn K-edge XANES and resulting lower coordination numbers estimated from analysis of the Zn K-edge data of ZnO heated at 500 °C, in comparison to bulk ZnO, suggest that the ZnO produced by this method has significant defects in the system.