Mesoporous Carbon from Optimized Date Stone Hydrochar by Catalytic Hydrothermal Carbonization Using Response Surface Methodology: Application to Dyes Adsorption

Providing efficient and environmental friendly ways to recover lignocellulosic waste remains a challenge around the world. In this study, citric acid-catalyzed hydrothermal carbonization (CHTC) was coupled with pyrolysis to convert date seed (Ds) into adsorbent material. In this regard, a central composite design (CCD) using response surface methodology (RSM) was developed to examine the influence of temperature, reaction time, and catalyst dose on the mass yield (Y-m(%)) and carbon retention rate (C-RR(%)) in the produced hydrochars. The optimized hydrochar (OHC-Ds) was obtained under optimal conditions (200 degrees C, 120 min, 20 mg) and characterized by a Y-m(%) and C-RR(%) of 59.71% and 75.84%, respectively. Chemical activation by KOH of OHC-Ds followed by pyrolysis at 600 degrees C resulted in an active material (AOHC-Ds) rich in carbon and characterized by a high specific surface area of 1251.5 m(2)/g, with the dominance of mesopores, as well as an amorphous structure comparable to graphite shown by X-ray diffraction (XRD) analysis. Adsorption experiments of two dyes on AOHC-Ds showed a high maximum adsorption capacity (Q(m)) of 657.89 mg g(-1) for methylene blue (MB) and 384.61 mg g(-1) for methyl orange (MO) compared to other conventional adsorbents. This result is due to the low acidity (pH(pzc)) of the surface of AOHC-Ds, which equals 6.75, and its surface, which is also rich in oxygenated functional groups such as (-OH), (C=O), and (C-O) shown by FTIR analysis. These results suggest that the coupling of CHTC and KOH activation followed by pyrolysis is an encouraging way to prepare an efficient and inexpensive adsorbent to remove dyes in wastewater.

Automated summary

Efficient and environmental friendly conversion of date seed into adsorbent material was achieved by coupling citric acid-catalyzed hydrothermal carbonization with pyrolysis. The optimized hydrochar exhibited high mass yield and carbon retention rate, while the chemically activated carbon material showed a high specific surface area and excellent adsorption capacity for dyes. The combination of CHTC and KOH activation followed by pyrolysis proves to be a promising method for preparing efficient and cost-effective adsorbents for wastewater treatment.