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

Arsenic (As) contaminants post tremendous threats to environment safety. Pristine hydrochar (PHC), thiourea-activated hydrochar (THC), and thiourea-Fe(NO)-activated hydrochar (FeO@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 (-NH, C-N, C=S and S=O). Fe(NO) introduced γ-FeO nanoparticles and provided FeO@THC with Fe-O. The combination of thiourea and Fe(NO) granted FeO@THC with the largest surface area (33.45 m/g), and the highest total pore volume (0.095 cm/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: FeO@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 FeO@THC, respectively. FeO@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.