In this study, the photocatalytic degradation of Methylene Blue was investigated using CdSe nanoparticles. CdSe nanoparticles were synthesized via a simple method and were characterized by FTIR, XRD, FESEM, BET, DRS and EDS techniques. The photocatalytic performance of the CdSe nanoparticles was optimized using Response Surface Methodology (RSM) under visible light. The independent variables involved initial pH, MB concentration, photocatalyst dosage, and irradiation time were evaluated and the optimum photodegradation efficiency of MB dye removal was achieved ˜ 92.80% at pH = 8, 20 mgL⁻¹ of MB concentration, 0.02 g 50 mL⁻¹ of CdSe dosage, and 20 min of irradiation time. Also, the photodegradation of MB by CdSe is obeyed pseudo-first-order kinetic model (k = 0.038 min⁻¹). The thermodynamic results revealed that the photocatalytic degradation of MB is spontaneous and endothermic. Also, the evaluation of various scavengers confirmed that the MB photodegradation was mainly done by photogenerated holes and hydroxyl radicals.

In this study, a flower-like SnIn₄S₈/SmVO₄ heterostructure was synthesized by applying a hydrothermal approach and used as a visible-light-driven photocatalyst to remove hexavalent chromium (Cr⁶⁺) and Rhodamine B (RhB). The process design and optimization were carried out by response surface methodology (RSM). An artificial neural network (ANN) was also used to determine the relative importance of operational factors. Under RSM-based optimal conditions, the Cr⁶⁺ and RhB removal efficiency reached 90.93 and 97.57%, respectively. Process modeling by ANN revealed pH as the most influential factor in Cr⁶⁺ and dye removal. The predominant photocatalytic activity of SnIn₄S₈/SmVO₄ was attributed to its Z-scheme structure, leading to the significant separation of charge carriers and conserving the redox capacity of the photogenerated electron-holes. Kinetic studies revealed that the SnIn₄S₈/SmVO₄ could achieve considerable rate constants of 0.036 and 0.080 min⁻¹ to remove Cr⁶⁺ and RhB, respectively. Furthermore, the catalyst’s reusability was confirmed under optimal conditions.

The adsorption characteristics of 4-chloro-2-nitrophenol (4C2NP) onto single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs) from aqueous solution were investigated with respect to the changes in the contact time, pH of solution, carbon nanotubes dosage and initial 4C2NP concentration. Experimental results showed that the adsorption efficiency of 4C2NP by carbon nanotubes (both of SWCNTs and MWCNTs) increased with increasing the initial 4C2NP concentration. The maximum adsorption took place in the pH range of 2–6. The linear correlation coefficients of different isotherm models were obtained. Results revealed that the Langmuir isotherm fitted the experimental data better than the others and based on the Langmuir model equation, maximum adsorption capacity of 4C2NP onto SWCNTs and MWCNTs were 1.44 and 4.42 mg/g, respectively. The observed changes in the standard Gibbs free energy, standard enthalpy and standard entropy showed that the adsorption of 4C2NP onto SWCNTs and MWCNTs is spontaneous and exothermic in the temperature range of 298–328 K.

This study presents the preparation of SiO₂/g-C₃N₅@NiFe₂O₄ nanophotocatalyst for the removal of betamethasone from aqueous solutions. The SiO₂/g-C₃N₅@NiFe₂O₄ nanophotocatalyst was synthesized using the solvothermal method, and its structure and optical properties were characterized and confirmed through XRD, FESEM, EDX, DRS, BET, VSM and PL analysis. Photocatalytic removal of betamethasone was optimized using a central composite design. The band gap of pure g-C₃N₅, NiFe₂O₄, and SiO₂/g-C₃N₅@NiFe₂O₄ was obtained 2.4 eV, 2.7 eV, and 1.4 eV, respectively using the Tauc plot. The F-value of 909.88 and Lack of Fit F-value of 0.41 confirm the obtained model is significant. Also, the value of R² = 0.9988 along with R²adja = 09977 demonstrates excellent model performance. Maximum removal efficiency of betamethasone was approximately 87.15% under the following optimal conditions: nanophotocatalyst dosage of 0.005 g/50 mL, a betamethasone concentration of 20 mg/L, and an irradiation time of 40 min under visible light. This performance closely aligns with the actual value of 80.65%. In conclusion, the SiO₂/g-C₃N₅@NiFe₂O₄ nanophotocatalyst demonstrates excellent photocatalytic ability for the removal of betamethasone from aqueous solutions.