UV modification of biochar for enhanced hexavalent chromium removal from aqueous solution

Abstract

This study was conducted to understand the effects of ultraviolet (UV) irradiation on the physicochemical properties and the hexavalent chromium (Cr(VI)) removal ability of biochar. Structural and morphological analysis showed that UV irradiation increased the specific surface area of biochar and added a large amount of oxygen-containing functional groups (e.g., carboxyl, lactonic, and hydroxyl) to biochar's surface. Batch sorption experimental results showed that UV-modified biochar (UVBC) produced at the pyrolysis temperature of 300 °C, the irradiated time of 24 h, and the irradiation distance of 40 mm exhibited excellent Cr(VI) removal ability (from 1.11 mg/g for BC to 20.04 mg/g for UVBC, a 18.1-fold increase). The adsorption kinetics and adsorption isotherm data agreed well with the pseudo-second-order model and Freundlich model, respectively. Experimental and modeling results suggest that the oxygen-containing functional groups and specific surface areas of biochars were notably increased by UV irradiation, which enhanced Cr(VI) adsorption by surface complexation. X-ray photoelectron spectroscopy (XPS) analysis of UVBC before and after reaction with Cr(VI) showed that reduction occurred during Cr(VI) adsorption. The energy consumption of UV modification is 2.7 MJ per gram of UVBC produced, which is comparable to that in activated carbon. The results showed that the method of UV modification of biochar is a very novel and effective method for the adsorption of Cr(VI) in solution.

Mechanism of Cr(VI) removal by magnetic greigite/biochar composites

“…However, the pristine biochars, acquired from direct biomass pyrolysis, often have relatively low adsorptive and reductive ability for Cr(VI), but these properties are dependent on biomass feedstock and pyrolysis temperature (Dong et al, 2011;Jin et al, 2016;Zhang et al, 2018). Thus, specific activation processes, such as surface functionalization, molecular grafting, ultraviolet irradiation and ball milling, have been used to enhance the Cr(VI) removal performance of biochars (Peng et al, 2018;Zhang et al, 2019b;Zhao et al, 2017;Zhu et al, 2018b). These modifications not only increase surface adsorption sites, but also change surface charge and functional group characteristics that regulate Cr(VI) adsorption and reduction dynamics.…”

Removal of aqueous Cr(VI) by magnetic biochar derived from bagasse

“… Adsorbent Q max (mg g −1 ) pH Conc. (mg L −1 ) BET (m 2 g −1 ) T (K) References MNA-S 15.6 2.5 20–50 152.6 298 46 MNA-L 11.1 2.5 20–50 34.4 298 46 microalgal based materials 25.19 2 1–10 295 47 UV-modified biochar 20.04 Natural pH 20 298 48 Melia azedarach wood magnetic biochar 25.27 3.0 5–200 5.219 298 48 Oak wood char 4.62 2.0 1–100 1–3 298 22 Oak bark char 4.61 2.0 1–100 1.88 298 22 Astragalus mongholicus magnetic biochar 23.85 …”

Biochar modification methods and mechanisms for salt‐affected soil and saline‐alkali soil improvement: A review

“…It has been reported that UV treatment enhances polar functionalities like carboxyl groups and reduces the pH of BC, leading to a reduced effect in raising soil pH (Figure 6) (Peng et al., 2018; Zhang et al., 2021). Other physical modification methods such as ultrasonic and microwave modifications are still uncertain because no researchers have investigated their potential effects on saline‐alkali soil remediation.…”