Arsenic removal via a novel hydrochar from livestock waste co-activated with thiourea and γ-Fe2O3 nanoparticles

Abstract

Arsenic (As) contaminants post tremendous threats to environment safety. Pristine hydrochar (PHC), thiourea-activated hydrochar (THC), and thiourea-Fe(NO3)3-activated hydrochar (Fe2O3@THC) were fabricated from dairy cattle manure via one-pot hydrothermal carbonization at 250 ℃ and applied for aqueous As(V) removal. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were conducted to characterize hydrochars and As(V) adsorption. Thiourea increased N and S functional groups (–NH2, C–N, C=S and S=O). Fe(NO3)3 introduced γ-Fe2O3 nanoparticles and provided Fe2O3@THC with Fe–O. The combination of thiourea and Fe(NO3)3 granted Fe2O3@THC with the largest surface area (33.45 m2/g), and the highest total pore volume (0.095 cm3/g) among three hydrochars. As(V) adsorption was a physicochemical process involving electrostatic attraction, complexation, ion exchange and H-bond interaction. The maximum As(V) adsorption capacities and partition coefficients decreased as follows: Fe2O3@THC (44.80 mg/g; 38.44 L/g) > THC (38.77 mg/g; 5.94 L/g) > PHC (19.05 mg/g; 1.17 L/g). Three hydrochars exhibited preferable reusability in NaOH solution with only 24.2%, 11.8% and 14.1% decrease in adsorption rates after four cycles for PHC, THC and Fe2O3@THC, respectively. Fe2O3@THC is a promising adsorbent for efficient As(V) removal. This study explored the efficient As(V) removal by activated hydrochars with future research potential.