Hydrothermal carbonization of spent coffee grounds: Hydrochar preparation, characterization, and adsorptive removal of rhodamine 6G

IF 7.3 2区环境科学与生态学 Q1 BIOTECHNOLOGY & APPLIED MICROBIOLOGY

Environmental Technology & Innovation Pub Date : 2026-03-01 Epub Date: 2025-12-30 DOI:10.1016/j.eti.2025.104731

Lucy Nyambura Karanja , Elsada Neziri , Anna Bulátkó , Rong Shan , Krisztina László , Imre Miklós Szilágyi

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引用次数: 0

Abstract

Hydrochars synthesized under different hydrothermal conditions were investigated to evaluate their structural properties and adsorption performance toward Rhodamine 6G (Rh 6G). Increasing hydrothermal temperature and residence time promoted the formation of a condensed carbon framework, consistent with progressive dehydration and aromatization. FTIR analysis revealed oxygen containing functional groups (-OH, CO, and CC), while EDX showed increasing carbon content and decreasing oxygen content with increasing hydrothermal severity. XRD patterns confirmed an amorphous structure, and nitrogen adsorption-desorption analysis indicated low BET surface areas of 2.0–4.53 m² g⁻¹.

Batch adsorption experiments showed rapid initial uptake of Rh 6G followed by equilibrium, with removal efficiencies of 72–96 %. Adsorption kinetics followed the pseudo-second-order model (R² = 0.991–0.9998), indicating surface-controlled adsorption. Equilibrium data fitted the Langmuir isotherm, suggesting monolayer adsorption, with maximum adsorption capacities of 299.21 ± 2.97–633.12 ± 12.17 mg g⁻¹. Thermodynamic analysis indicated spontaneous and endothermic adsorption, with enthalpy values of 20.81–27.71 kJ mol⁻¹ and positive entropy changes. Adsorption efficiency increased with increasing solution pH and adsorbent dosage. Post-adsorption FTIR spectra showed peak shifts and new bands, confirming surface functional group involvement in dye binding. Despite the low surface area, high adsorption performance was attributed to electrostatic attraction, π-π interactions, and hydrogen bonding. Reusability tests showed that the hydrochars retained approximately 85 % of their initial adsorption capacity after four cycles, demonstrating their potential as reusable adsorbents for dye-contaminated wastewater.

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废咖啡渣的水热碳化：水炭制备、表征和罗丹明6G的吸附去除

研究了在不同水热条件下合成的氢炭的结构性质和对罗丹明6G （Rh 6G）的吸附性能。水热温度和停留时间的增加促进了碳骨架的形成，与逐渐脱水和芳构化相一致。FTIR分析显示含氧官能团（-OH、CO和CC），而EDX随热液严重程度的增加，碳含量增加，氧含量减少。XRD谱图证实其为非晶态结构，氮气吸附-解吸分析表明BET比表面积在2.0 ~ 4.53 m2 g−1之间。间歇式吸附实验表明，Rh 6G的初始吸附快速，随后达到平衡，去除率为72-96 %。吸附动力学符合拟二阶模型（R2 = 0.991-0.9998），表明表面控制吸附。平衡数据符合Langmuir等温线，表明单层吸附，最大吸附量为299.21 ± 2.97-633.12 ± 12.17 mg g−1。热力学分析表明，吸附为自发吸热吸附，焓值为20.81 ~ 27.71 kJ mol−1，熵变为正。吸附效率随溶液pH和吸附剂用量的增加而增加。吸附后的FTIR光谱显示出峰移和新波段，证实了表面官能团参与了染料的结合。尽管比表面积小，但由于静电吸引、π-π相互作用和氢键的作用，其吸附性能很高。可重复使用性测试表明，经过四个循环后，水合物保留了约85% %的初始吸附容量，证明了它们作为可重复使用的染料污染废水吸附剂的潜力。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Environmental Technology & Innovation Environmental Science-General Environmental Science

CiteScore

14.00

自引率

4.20%

发文量

435

审稿时长

74 days

期刊介绍： Environmental Technology & Innovation adopts a challenge-oriented approach to solutions by integrating natural sciences to promote a sustainable future. The journal aims to foster the creation and development of innovative products, technologies, and ideas that enhance the environment, with impacts across soil, air, water, and food in rural and urban areas. As a platform for disseminating scientific evidence for environmental protection and sustainable development, the journal emphasizes fundamental science, methodologies, tools, techniques, and policy considerations. It emphasizes the importance of science and technology in environmental benefits, including smarter, cleaner technologies for environmental protection, more efficient resource processing methods, and the evidence supporting their effectiveness.