Green production of hydrochar nut group from waste materials in subcritical water medium and investigation of their adsorption performance for crystal violet

Abstract

This study evaluates the production of hydrochars from the outer shells of the nut group (peanut, hazelnut, walnut, and pistachio) in an eco-friendly subcritical water medium (SWM) and their effects as adsorbents on the removal of crystal violet (CV) from an aqueous solution. The prepared hydrochars were characterized using Brunauer Emmett-Teller (BET) analysis, scanning electron microscope (SEM), Fourier transforms infrared spectroscopy (FTIR), and zeta potential. The adsorption process was optimized based on pH, adsorbent dose, dye concentration, and contact time. The hazelnut hydrochar was found to have the maximum removal efficiency (91%). Optimum conditions were pH of 8, particle size <45 μm, adsorption time of 60 min, and dye concentration of 25 mg/L. The results of all hydrochars were fitted to the second-order kinetics. Langmuir, Freundlich, and Redlich-Peterson isotherms models were used to explain the relationship between adsorbent and adsorbate. For all hydrochars, CV adsorption was found to be feasible and inherently spontaneous. The use of materials with no commercial value like; the outer shells of the nut group, is considered a method for waste reduction using the SWM method. Practitioner Points• Hydrochars of nut group were synthesized in the subcritical water medium.• Adsorption ability of the hydrochars in the adsorption of crystal violet were investigated.• Adsorption isotherms were used to explain the relationship between adsorbent and adsorbate.• The hazelnut hydrochar provided the maximum removal efficiency (91%).• Hazardous water pollutant effectively removed using an eco-friendly method.

Adsorption of Direct Orange 46 and phosphate ions on waste tomato stem ash used as a bio‐based adsorbent

“…The dye adsorption capacity of tomato stem ash increased with decreasing particle size. As the particle size decreases, the surface area increases and effectively affects the adsorption of the pollutants 42 …”

“…As the particle size decreases, the surface area increases and effectively affects the adsorption of the pollutants. 42 F I G U R E 6 The effect of solution pH value on the adsorption process using tomato stem.…”

Leonardite powder as an efficient adsorbent for cationic and anionic dyes

“…Several researchers found that the pseudo‐second‐order model can describe the adsorption of dyes better than Lagergren's pseudo‐first‐order (Isik, Saleh, Bilici, & Dizge, 2021; Yalvaç et al, 2021). Saleh, Isik, Yabalak, et al (2021) prepared hydrochars from nuts group for crystal violet adsorption. All of the prepared hydrochars were found to follow the pseudo‐second‐order model.…”

“…However, many researchers have explored the adsorbent abilities of different material types to achieve better results at lower costs (Deb et al, 2020). Bio adsorbents (Gupta, 2009), zeolite (Brião et al, 2018), metal–organic frameworks (Xin et al, 2013), alumina (Banerjee et al, 2019), covalent organic frameworks (He et al, 2021), biochar (Ahmad et al, 2020), two‐dimensional materials (MXene) (Sun et al, 2021; Yang et al, 2021), modified activated carbon (Ho et al, 2019), and hydrochar (Saleh, Isik, Yabalak, et al, 2021) were broadly examined. Leonardite is the oxidation product of low‐quality coal (lignite) during carbonization.…”

Walnut Shell Biowaste Valorization via HTC Process for the Removal of Some Emerging Pharmaceutical Pollutants from Aqueous Solutions

“…Using various technologies, such as pyrolysis [ 3 ], combustion [ 4 ], anaerobic digestion [ 4 , 5 ], fermentation [ 6 ], etc., biowastes can be valorized into biofuels [ 7 , 8 ], bio-oil [ 9 ], valuable chemicals [ 10 , 11 ], and activated carbon-based adsorbents [ 12 , 13 , 14 , 15 , 16 , 17 ].…”