Key Takeaways & Executive Findings
- •• • HPR-AC achieved maximum adsorption capacities of 67.12 mg·g−1 for Sunset Yellow, 79.72 mg·g−1 for Ponceau 4R, and 72.75 mg·g−1 for Tartrazine at pH 5 and 55 °C, demonstrating high efficacy for azo dye removal from industrial wastewater. • • The adsorption process followed Langmuir isotherm and pseudo-second-order kinetics, indicating monolayer chemisorption with an endothermic nature, which is critical for designing energy-efficient treatment systems. • • Characterization via BET, FTIR, XRD, and XPS confirmed high specific surface area and abundant mesoporous structure, enabling rapid dye diffusion and enhanced adsorption capacity, essential for scalable water treatment applications. • • Statistical physics modeling revealed a multilayer physical adsorption mechanism dominated by pore filling, electrostatic interactions, hydrogen bonding, π-π stacking, and charge transfer, providing a mechanistic basis for optimizing adsorbent regeneration and process conditions.
Abstract
Azo food colorants are persistent aquatic pollutants posing risks to ecosystems and human health. Utilizing biomass waste to produce low-cost activated carbon offers a sustainable strategy for their removal. In this study, activated carbon (HPR-AC) was synthesized from Haematococcus pluvialis residue via phosphoric acid activation, and its adsorption performance was evaluated using Sunset Yellow (SY), Ponceau 4R (P4R), and Tartrazine (TY) as model pollutants. The effects of solution pH, adsorbent dosage, initial dye concentration, and temperature on adsorption efficiency were systematically examined. Characterization by BET, FTIR, XRD, and XPS revealed that HPR-AC possesses a high specific surface area and an abundant mesoporous structure. The adsorption process was well described by the Langmuir isotherm and pseudo-second-order kinetic models, indicating monolayer chemisorption and an endothermic nature. At pH 5 and 55 °C, the maximum adsorption capacities reached 67.12, 79.72, and 72.75 mg·g−1 for SY, P4R, and TY, respectively. Statistical physics modeling further suggested a multilayer physical adsorption mechanism, primarily governed by pore filling, electrostatic interactions, hydrogen bonding, π-π stacking, and charge transfer. These findings provide both theoretical insights and empirical data for the valorization of H. pluvialis residue and the development of efficient, sustainable adsorbents for azo dye removal from water.
1. Introduction
The pervasive use of azo food colorants such as Sunset Yellow, Ponceau 4R, and Tartrazine in the food industry has led to their frequent detection in aquatic environments. These compounds are resistant to conventional biodegradation and oxidation, posing long-term ecological and health risks due to their potential to form carcinogenic aromatic amines. Existing treatment methods, including chemical oxidation, electrocoagulation, and membrane filtration, often suffer from high operational costs, secondary pollution, or membrane fouling, limiting their practical application. The development of low-cost, high-efficiency adsorbents from biomass waste presents a promising alternative, aligning with circular economy principles.
This study addresses the bottleneck by synthesizing activated carbon from Haematococcus pluvialis residue, a byproduct of astaxanthin extraction, via phosphoric acid activation. The resulting HPR-AC exhibits a high specific surface area and mesoporosity, enabling efficient adsorption of three representative azo dyes. Systematic investigation of pH, dosage, concentration, and temperature effects, coupled with advanced characterization and statistical physics modeling, provides a comprehensive understanding of the adsorption mechanisms. These findings not only valorize an underutilized biomass waste but also offer a sustainable and cost-effective solution for azo dye remediation in industrial effluents.
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MENG Yifan, LI Xingchao, ZHANG Lei, SONG Xueer, HU Xinyue, WANG Yue, WANG Menghan, LI Zichao (2026). Efficient Adsorption of Food Colorants onto Activated Carbon Derived from Haematococcus pluvialis Residue: Performance and Mechanism. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2026050701
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Frequently Asked Questions
What is the maximum adsorption capacity of HPR-AC for Sunset Yellow, Ponceau 4R, and Tartrazine under optimal conditions?
Under optimal conditions of pH 5 and 55 °C, HPR-AC exhibits maximum adsorption capacities of 67.12 mg·g−1 for Sunset Yellow, 79.72 mg·g−1 for Ponceau 4R, and 72.75 mg·g−1 for Tartrazine, as determined by Langmuir isotherm fitting.
What are the dominant adsorption mechanisms of HPR-AC for azo dyes?
Statistical physics modeling indicates a multilayer physical adsorption mechanism, primarily governed by pore filling, electrostatic interactions, hydrogen bonding, π-π stacking, and charge transfer. This is supported by characterization data showing high surface area and mesoporosity.
How does solution pH affect the adsorption efficiency of HPR-AC?
The adsorption efficiency is pH-dependent, with optimal performance observed at pH 5. At this pH, electrostatic interactions between the positively charged adsorbent surface and negatively charged dye molecules are maximized, enhancing adsorption capacity.
Is the adsorption process endothermic or exothermic?
The adsorption process is endothermic, as indicated by increased adsorption capacity at higher temperatures (up to 55 °C). This suggests that elevated temperatures enhance the adsorption kinetics and capacity, which is beneficial for industrial applications where warm effluents are common.
What is the regeneration potential of HPR-AC for repeated use?
While the study does not explicitly report regeneration data, the multilayer physical adsorption mechanism suggests that adsorbed dyes could be desorbed under appropriate conditions (e.g., pH adjustment or solvent washing), potentially allowing for multiple cycles. Further studies are needed to quantify regeneration efficiency and long-term stability.
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