The reaction time, temperature, ratio of precursors, and concentration of sodium citrate are known as the main factors that affect the direct synthesis process of SiO2@Au based on the chemical reaction of HAuCl4 and sodium citrate. Hence, we investigated, in detail, and observed that these factors played a crucial role in determining the shape and size of synthesized nanoparticles. The significant enhancement of the SERS signal corresponding to the fabrication conditions is an existing challenge. Our study results show that the optimal reaction conditions for the fabrication of SiO2@Au are a 1:21 ratio of HAuCl4 to sodium citrate, with an initial concentration of sodium citrate of 4.2 mM, and a reaction time lasting longer than 6 h at a temperature of 80 °C. Under optimal conditions, our synthesis process result is SiO2@Au nanoparticles with a diameter of approximately 350 nm. In particular, the considerable enhancement of Raman intensities of SiO2@Au compared to SiO2 particles was examined.

In this study, biochar derived from Jackfruit peel (JA) via the pyrolysis at 500 °C for 2 h was used as an adsorbent to remove Methylene Blue (MB) from aqueous solution. Effects of pH, contact time, and initial MB concentration were investigated. Isotherm models, such as Langmuir, Freundlich, Sips, and Dubinin-Radushkevich, were applied to estimate the adsorption in nature. The results indicated that the Sips and Freundlich models gave the best fit with experimental datas. The maximum adsorption capacity of MB calculated from Langmuir was 39.87 mg/g at 306K, pH = 11, and time = 60 min. The E value evaluated from Dubinin-Radushkevich smaller than 8 kJ/mol indicated that the MB adsorption of JA followed a physical process.

Kinetic studies play an instrumental role in determining the most appropriate reaction rate model for industrial-scale applications. This study focuses on the kinetics methylene blue (MB) adsorption from aqueous solutions by biochar derived from jackfruit peel. Various kinetic models, including pseudo-first-order (PFO), pseudo-second-order (PSO), intra-diffusion, and Elovich models, were applied to study MB adsorption kinetics of jackfruit peel biochar. The experiments were performed with two initial concentrations of MB (24.23 mg/L and 41.42 mg/L) over a span of 240 min. Our findings emphasized that the Elovich model provided the best fit of the experimental data for MB adsorption. When compared to other materials, biochar from jackfruit peel emerges as an eco-friendly adsorbent for dye decolorization, with potential applications in the treatment of environmental pollution.