Study on adsorption mechanism of silicate adsorbents with different morphologies and pore structures towards formaldehyde in water

Silicate with various pore structures and morphologies showed different adsorption effects on removing organic pollutants, but the corresponding adsorption mechanisms are ambiguous. In this work, the adsorption mechanisms of formaldehyde in water by silicate adsorbents with different morphologies and pore structures were investigated. Diatomite with disc-like morphology and calcium silicate with short rod-like morphology were selected for comparison. Results show that the adsorption capacity of calcium silicate with superior specific surface area and pore volume is higher than that of Diatomite. The pseudo-first-order and pseudo-second-order models were employed to fit the dynamics behaviors of adsorption process, and the pseudo-second-order model was more suitable one. Furthermore, the adsorption data was also modeled by the internal particle diffusion model and it was found that the adsorption process could be divided into surface fast adsorption and internal particle diffusion. The adsorption mechanism of diatomite on formaldehyde includes surface adsorption and internal particle diffusion, while surface adsorption is the main mechanism of removing formaldehyde by calcium silicate. Four adsorption isotherm models are used to describe the isotherm adsorption process, while Freundlich isotherm shows the best fit results, which indicates that both adsorbents are multilayer adsorption. It can be classified as physical adsorption.