Biochar colloids and their use in contaminants removal

In this study, we report on the extraction, characterization, and potential applications of colloidal biochar derived from pyrolyzed wood-an untapped source of carbonaceous particles.A series of characterizations was performed on biochar colloids to unravel their colloidal properties and surface chemistry through which it was found that they have a net negative charge and are stable between pH 3 and 10.Moreover,our initial toxicity tests showed that biochar colloids themselves are not toxic and they can be used in remediation applications,which led us to investigate(1)their copper sorption,a model inorganic contaminant,in a scenario that biochar colloids are released into the environment and(2)their potential use in organic pollutants adsorption and degradation.Copper sorption studies showed that biochar colloids have a copper sorption capacity as high as 22 mg g^(−1) in sub-ppm copper solutions.This increased the acute 48 h lethal concentration(LC50)of copper for Daphnia magna by 21 ppb,which is comparable to the previously reported effect by dissolved organic matter.Adsorption and degradation of methylene blue(MB),an often-used proxy for organic contaminants in water,were studied by coupling the biochar colloids to positively charged TiO_(2) nanoparticles and using it as a photocatalyst.The hybrid MB photodegradation efficiency was 21%higher than that of TiO_(2) nanoparticles alone.Enhancement of demethylation is proposed as the main degradation mechanism of MB,as confirmed by liquid chromatography-mass spectroscopy(LC/MS),and the positive impact of biochar colloids is ascribed to their abundant adsorption sites,which may facilitate MB adsorption and its photocatalytic degradation.