This work describes the hydroxyapatite nanoparticle (HAP) preparation from eggshell waste and their application as an adsorbent for Cephalexin (Ceph) antibiotic removal from aqueous solutions. Chemical precipitation with phosphoric acid was used to evaluate the feasibility of calcium oxide for HAP preparation. The structural properties of HAP were characterized by X-ray diffraction, which revealed the formation of the hydroxyapatite crystalline phase formation. In addition, transmitting electron spectroscopy showed an irregular shape with a variation in size. The impact of various experimental conditions on the removal efficiency such as the solution’s pH, contact time, HAP mass, solution temperature, and Ceph concentration were studied. Experimental data showed that HAP could remove most Ceph species from aqueous solutions within 1 h at pH = 7 with 70.70% adsorption efficiency utilizing 50 mg of the HAP. The removal process of Ceph species by HAP was kinetically investigated using various kinetic models, and the results showed the suitability of the pseudo-second-order kinetic model for the adsorption process description. Moreover, the removal process was thermodynamically investigated; the results showed that the removal was spontaneous endothermic and related to the randomness increase. The data confirmed that HAP had high efficiency in removing Ceph antibiotics from an aqueous solution.

In this study, we used density functional theory (DFT) and natural bond orbital (NBO) analysis to determine the structural, electronic, reactivity, and conformational features of 2,5,5-trimethyl-1,3,2-di-heteroatom (X) phosphinane-2-sulfide derivatives (X = O (compound 1), S (compound 2), and Se (compound 3)). We discovered that the features improve dramatically at 6-31G** and B3LYP/6-311+G** levels. The level of theory for the molecular structure was optimized first, followed by the frontier molecular orbital theory development to assess molecular stability and reactivity. Molecular orbital calculations, such as the HOMO–LUMO energy gap and the mapping of molecular electrostatic potential surfaces (MEP), were performed similarly to DFT calculations. In addition, the electrostatic potential of the molecule was used to map the electron density on a surface. In addition to revealing molecules’ size and shape distribution, this study also shows the sites on the surface where molecules are most chemically reactive.

A green synthesis method for producing zinc oxide nanoparticles (ZnO NPs) was presented using natural Gum Arabic (GA) as a natural stabilizing agent. For the first time, the as-synthesized ZnO NPs were employed to photodegrade the toxic Congo Red (CR) dye in an aqueous solution. The structural and morphological characterizations confirmed the successful synthesis of ZnO NPs. The ZnO NPs possessed an average crystallite size of 42.7 nm. In addition, it was found that a concentration of 20 mg L⁻¹ of CR dye yielded the most favorable photodegradation results, and 4 mg mL⁻¹ of the photocatalyst was the optimal amount. The results showed a maximum degradation percentage of 99.5% at pH 8 after 30 min of irradiation. This indicates that the as-synthesized ZnO NPs have remarkable photocatalytic properties. Moreover, the study demonstrated the suitability of the pseudo-first-order kinetic model for representing the photodegradation process through kinetic studies of the photocatalyst process of CR dye by ZnO NPs using the Langmuir-Hinshelwood (L-H) model.

Antibiotic pollution has become a serious concern due to the extensive use of antibiotics, their resistance to removal, and their detrimental effects on aquatic habitats and humans. Hence, developing an efficient antibiotic removal process for aqueous solutions has become vital. Amoxicillin (Amox) is one of the antibiotics that has been efficiently removed from an aqueous solution using hydroxyapatite nanoparticles (HAP NPs). The current study synthesizes and utilizes hydroxyapatite nanoparticles as a cost-effective adsorbent. Adsorbent dose, pH solution, initial Amox concentration, equilibrium time, and temperature are among the factors that have an evident impact on Amox antibiotic adsorption. The (200) mg dose, pH (5), temperature (25) °C, and time (120) min are shown to be the best-optimized values. The nonlinear Langmuir’s isotherm and pseudo-second-order kinetic models with equilibrium capacities of 4.01 mg/g are highly compatible with the experimental adsorption data. The experimental parameters of the thermodynamic analysis show that the Amox antibiotic adsorption onto HAP NPs powder is spontaneous and exothermic.

Cyclic voltammetry is a widely used technique in electrochemistry due to its simplicity and large amount of data and information that can be obtained. This study utilises this technique to study chlorophyll a and total chlorophyll (Tchl) alongside a laser light to induce photosynthesis. No oxidative peak was observed, regardless of the solution pH in either a dark or light environment when using a solution with an electrolyte of tetrabutylammonium perchlorate (TBAP) in both dichloromethane (DCM) and acetonitrile (MeCN), whereas in a solution of aqueous HCl a small anodic peak was observed. The concentration of the droplet of Tchl pigment on the surface of macro glassy carbon electrode (GCE) was increased, which resulted in a similar trend and the oxidation peak was observed to be slightly larger when in the presence of light. It was observed that the filtered solution of Tchl pigment produced a weaker signal than the unfiltered solution and there were slightly reduced oxidative peak currents when the concentration of VK₁ was increased. were no observed changes in the peak charges or currents over a wide potential range (0.0, 0.2, 0.4, 0.6 and 0.8 V) in the presence or absence of light by using coulometry and amperometry methods, therefore, more information on the 3-D formation is required for the photoreduction processes.

This chapter discusses the method of detection and separation of the fourth group cations, precipitate format, the impact of pH on the procedure.