Cost-effective eggshell-modified LDH composite for caffeine adsorption, cytotoxicity and antimicrobial activity: exploring the synergy and economic viability in search processes

Abstract

The rise of pharmaceutical residues poses a serious threat to ecological and aquatic environments, necessitating the development of cost-effective, convenient, and recyclable adsorbents. Given the high global consumption of eggs, a significant amount of waste eggshell is produced. The techniques outlined here aim to manage eggshell waste by transforming it into highly valuable products, addressing the issue of eggshell waste in communities and industries. This approach supports the concept of zero-waste operations to create value-added goods, contributing to sustainable development. In the future, this method of waste management and material recycling may be adopted as an alternative. CaO-based ZnFe-layered double hydroxide (LDH) is identified as an efficient adsorbent for caffeine (COF) residues due to its biodegradability and biocompatibility. We extensively analyzed the synthesized CaO, ZnFe-LDH, and CaO/ZnFe-LDH composites before the adsorption processes using FT-IR, XRD, SEM, EDX, BET surface area, PZC, TGA/DTG, and after the adsorption processes using FT-IR. We investigated factors affecting the adsorption process, such as pH, adsorbent dose, COF concentrations, and time. Six non-linear adsorption isotherm models were studied at pH 7 for the composite and pH 9 for LDH, showing maximum adsorption capacities (q_max) of 152.35 mg g⁻¹ for LDH and 194.87 mg g⁻¹ for CaO/ZnFe-LDH. Kinetic studies were also conducted. Interestingly, the MTT assay conducted on WI-38 cells revealed minimal toxicity, with most tests indicating cell viability above 60%. The synthesized CaO, ZnFe-LDH, and CaO/ZnFe-LDH composite exhibit robust antimicrobial properties against two pathogens, including Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (MRSA). The MIC values for the synthesized materials range from 0.87 to 7 µg mL⁻¹, varying with the microbial species. Two green metrics were applied: the analytical Eco-scale and the Analytical GREEnness Calculator (AGREE).