Bagasse Heavy Ash Valorization into Superhydrophobic Mesoporous Silica with Enhanced Air Permeability

To achieve sustainable development goals, concepts such as circular economy, green economy, and sharing economy are applied to reduce resource consumption as necessary. In this context, silica sand, traditionally the sole source for sodium silicate preparation, is being reconsidered as substitution with bagasse ash waste. The challenges arising from the accumulated quantity of bagasse heavy ash and the recurrent flooding impact on woody perennials, faced by farmers, have been addressed. To enhance hydrophobicity, the synthesis processes of mesoporous silica from bagasse heavy ash-derived sodium silicate were modified by incorporating varying amounts (0.5-5.0 g salt/g SiO2) of NaCl, KCl, MgCl2, and CaCl2. Surface hydrophobicity was further improved by functionalizing with trimethylchlorosilane (TMCs) in n-hexane (0.00-5.00% v/v). The obtained products were systematically characterized for their textural and structural characteristics, contact angle, and air transmission under flooding conditions. The addition of small amounts of NaCl, KCl, and MgCl2 reduced the silanol groups in the structure, leading to an increase in hydrophobic properties. In addition, alkaline earth chlorides (MgCl2 and CaCl2) led to the formation of bimodal mesopores. Particularly, MgCl2 effectively decreased silanol groups to an appropriate level for silylation with TMCs, reducing TMCs consumption for surface functionalization by 80%. The resultant functional porous silica exhibited remarkable hydrophobicity, with a water contact angle as high as 125 degrees. After the forming process, the obtained rod-shaped silane-functionalized porous silica modified with 5.0 g of MgCl2 exhibited 1.37 times higher oxygen transfer efficiency, compared to unmodified silica. These functionalized porous silica materials offer an effective solution to the challenges of sustainably utilizing accumulated bagasse ash. They significantly reduce environmental impact, decreasing terrestrial ecotoxicity and land use by 15.1% and 14.9%, respectively, compared to conventional production routes using silica sand. The innovative production of these functional porous silica with hydrophobic properties holds commercial value and aligns well with circular and green economy principles.