ABSTRACT

Safranin orange (SO) is a cationic dye widely used in industrial sectors. It becomes a threat to the aquatic ecosystem once it reaches water resources, directly affecting photosynthetic activity and dissolved oxygen rate. In view of this scenario and considering the large production of agro-industrial waste, which provides significant disposal costs and environmental impacts, the agricultural by-products such as mandarin peels (MP) are being used as biosorbent materials. Thus, this work proposed the use of MP for SO adsorption. The material was characterized by SEM, zeta potential, and FTIR analysis, in which it was possible to verify heterogeneous porous morphology, predominantly negative surface, and organic functional groups that facilitate adsorption. The results were promising, wherein the maximum adsorption capacity was 464 mg g^–1 (318 K), 0.4 g L^–1 adsorbent concentration, 120 min equilibrium time and removal percentage of 84.75%. The experimental data showed a better fit to the Langmuir and pseudo-second order mathematical models. The thermodynamic analysis inferred spontaneous, endothermic, and reversible character for SO adsorption onto MP. The main proposed adsorptive mechanisms were hydrogen bonds, π-interactions, and electrostatic interactions. In addition, the reuse of MP showed good efficiency since the adsorption capacity was maintained above 50% after four cycles (from 77.90 to 41.55 mg g^–1). Moreover, when evaluating the effect of pH and ionic strength, it verified that the adsorption efficiency was not reduced. Therefore, when compared with other materials, the versatility and potential applicability of MP as a low-cost adsorbent for wastewater treatment is notable.

摘要

番红橙（SO）是一种广泛应用于工业领域的阳离子染料。一旦到达水资源，就会对水生生态系统构成威胁，直接影响光合活性和溶解氧率。鉴于这种情况并考虑到大量生产的农业工业废物，这会带来巨大的处置成本和环境影响，因此正在使用橘子皮 (MP) 等农业副产品作为生物吸附材料。因此，这项工作提出了使用 MP 吸附 SO。该材料通过 SEM、zeta 电位和 FTIR 分析进行了表征，其中可以验证异质多孔形态、主要为负表面和促进吸附的有机官能团。结果是有希望的，其中最大吸附容量为464 mg g^–1 (318 K)，0.4 g L ^–1吸附剂浓度，120 min 平衡时间和 84.75% 去除率。实验数据显示更适合朗缪尔和伪二阶数学模型。热力学分析推断出 SO 吸附到 MP 上的自发、吸热和可逆特性。主要提出的吸附机制是氢键、π-相互作用和静电相互作用。此外，由于四次循环后吸附容量保持在 50% 以上（从 77.90 到 41.55 mg g ^-1）。此外，在评估 pH 值和离子强度的影响时，证实吸附效率没有降低。因此，与其他材料相比，MP 作为废水处理的低成本吸附剂的多功能性和潜在适用性是显着的。