Biomass-derived activated carbons from date pits and spirulina for CO₂ and water vapor adsorption: a comparative study of uptake ratios

Abstract

Increasing emissions of greenhouse gases, such as CO₂, cause a rise in the average temperature of the Earth’s climate system. It is well established that ZnCl₂ activation or treatment is one of the most widely used methods for maximizing CO₂ adsorption capacity. However, water vapor co-adsorption during CO₂ capture processes can result in higher regeneration energies. This study aims to evaluate the effectiveness of ZnCl₂-activated carbons coated with a thin layer of vinyltrimethoxysilanein to increase the CO₂/H₂O uptake ratio. Date pits and Spirulina were used separately to produce activated carbons. The CO₂ adsorption capacities of the samples were investigated using thermogravimetric analysis with 15% CO₂ in nitrogen, while the water vapor uptake at 10, 50, and 95% relative humidity (RH) was investigated using Dynamic Vapor Sorption. Partial reductions in specific surface area and pore volume occurred after silane modification. However, heat treatment of the coated samples at 450 ^oC, which moderated the coating layer on the surface and reopened some of the blocked pores, increased the CO₂/H₂O uptake ratio, especially for the activated carbon derived from date pits (DPZHC), to 3.01 at 10% RH. Therefore, this sample is a promising candidate for co-adsorption processes. Although the study was conducted under controlled conditions, the adsorbent's stability and its ability to regenerate and be reused still need to be determined.