Pyrolyzed biomass-derived nanoparticles:a review of surface chemistry,contaminant mobility,and future research avenues to fill the gaps

Nanoparticles are abundant in the subsurface,soil,streams,and water bodies,and are often a critical control on elemental speciation,transport and cycling in the natural environment.This review provides an overview of pyrolyzed biomass-derived nanoparticles(PBNPs),their surface properties and reactivity towards aqueous species.We focus specifically on biochar-derived nanoparticles and activated carbon-derived nanoparticles which fall under our classification of PBNPs.Activated carbon-iron(nano)composites are included in some instances where there are significant gaps in literature because of their environmental relevance.Increased use of activated carbon,along with a resurgence in the manufacture and application of biochar for water treatment and soil amendment,has generated significant concerns about the mobility and toxicity of PBNPs derived from the bulk material in environmental applications.Recent examples are discussed to highlight current progress in understanding the influence of PBNPs on contaminant transport,followed by a critical discussion of gaps and future research directions.

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.