Introduction of N-containing moieties by ammonia plasma technique can substantially improve ciprofloxacin removal by biochar and the associated mechanisms: Spectroscopic and site energy distribution analysis

Synthesis of porous carbon derived from coal tar residue via bimetallic salt activation for effective and selective adsorption of thallium(I)

As a highly toxic rare metal, the removal of thallium (Tl) from wastewater has been widely investigated, and adsorption is considered one of the most promising treatment technologies for Tl-containing contaminated water because of its cost-effectiveness, convenience, and high efficacy. In this work, coal tar residue (CTR)-based porous carbon was synthesized through K2FeO4 activation, and applied in adsorbing Tl(I). K2FeO4 could synergistically produce porosity and load iron oxide on the produced porous carbon surface because of the catalytic cracking and oxidative etching during the activation of CTR. The adsorbent was synthesized at 800 ℃ with a mass ratio of K2FeO4/CTR being 3 (PC3-800) showed optimal Tl(I) adsorption performance. The removal efficiency and distribution coefficient of PC3-800 were above 95 % and 104 mL/g, respectively, in a wide pH range (4-10). Furthermore, the selection and reusability of PC3-800 were favorable. The adsorption was a spontaneous, exothermic, and entropy increase process. The adsorption process was dominated by electrostatic attraction, surface complexation, and surface oxidation. The results suggested that removing Tl(I) from contaminated water via CTR-based porous carbon was feasible.

Adsorption and photocatalytic degradation of quinolone antibiotics from wastewater using functionalized biochar

Quinolone antibiotics are emerging environmental contaminants, which cause serious harm to the ecological environment and human health. How to effectively remove these emerging pollutants from water remains a major challenge worldwide. In this study, a novel Fe/Ti biochar composite (Fe/Ti-MBC) was prepared by facile one-step co-pyrolysis of wood chips with hematite and titanium dioxide (TiO2) for adsorption and photocatalytic degradation of ciprofloxacin (CIP) and norfloxacin (NOR) in water. The results showed that the degradation efficiencies of Fe/Ti-MBC to CIP and NOR were 88.4% and 88.0%, respectively. The π-π interactions and polar interactions are the main adsorption mechanisms for CIP and NOR. In the photocatalytic process, h+ and ·OH are the main active substances for the oxidative degradation of CIP and NOR. This study shows that Fe/Ti-MBC is an effective and recyclable composite, providing a novel alternative way for antibiotics degradation.

Revealing the role of calcium alginate-biochar composite for simultaneous removing SO42- and Fe3+ in AMD: Adsorption mechanisms and application effects

The remediation of acid mine drainage (AMD) is particularly challenging because it contains a large amount of Fe³⁺ and a high concentration of SO₄^2-. To reduce the pollution caused by SO₄^2- and Fe³⁺ in AMD and realize the recycling of solid waste, this study used distillers grains as raw materials to prepare biochar at different pyrolysis temperatures. Calcium alginate-biochar composite (CA-MB) was further synthesized via the entrapment method and used to simultaneously remove SO₄^2- and Fe³⁺ from AMD. The effects of different influencing factors on the sorption process of SO₄^2- and Fe³⁺ were studied through batch adsorption experiments. The adsorption behaviors and mechanisms of SO₄^2- and Fe³⁺ were investigated with different adsorption models and characterizations. The results showed that the adsorption process of CA-MDB600 on SO₄^2- and Fe³⁺ could be well described by Elovich and Langmuir-Freundlich models. It was further proved by the site energy analysis that the adsorption mechanisms of SO₄^2- onto CA-MDB600 were mainly surface precipitation and electrostatic attraction, while that of Fe³⁺ removal was attributed to ion exchange, precipitation, and complexation. The applications of CA-MDB600 in actual AMD proved its good application potential. This study indicates that CA-MDB600 could be applied as a promising eco-friendly adsorbent for the remediation of AMD.

Degradation of atrazine in river sediment by dielectric barrier discharge plasma (DBDP) combined with a persulfate (PS) oxidation system: response surface methodology, degradation mechanisms, and pathways

Single degradation systems based on dielectric barrier discharge plasma (DBDP) or persulfate (PS) oxidation cannot achieve the desired goals (high degradation efficiency, high mineralization rate, and low product toxicity) of degrading atrazine (ATZ) in river sediment. In this study, DBDP was combined with a PS oxidation system (DBDP/PS synergistic system) to degrade ATZ in river sediment. A Box-Behnken design (BBD) including five factors (discharge voltage, air flow, initial concentration, oxidizer dose, and activator dose) and three levels (- 1, 0, and 1) was established to test a mathematical model by response surface methodology (RSM). The results confirmed that the degradation efficiency of ATZ in river sediment was 96.5% in the DBDP/PS synergistic system after 10 min of degradation. The experimental total organic carbon (TOC) removal efficiency results indicated that 85.3% of ATZ is mineralized into CO₂, H₂O, and NH₄⁺, which effectively reduces the possible biological toxicity of the intermediate products. Active species (sulfate (SO₄•^-), hydroxy (•OH), and superoxide (•O₂^-) radicals) were found to exert positive effects in the DBDP/PS synergistic system and illustrated the degradation mechanism of ATZ. The ATZ degradation pathway, composed of 7 main intermediates, was clarified by Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS). This study indicates that the DBDP/PS synergistic system is a highly efficient, environmentally friendly, novel method for the remediation of river sediment containing ATZ pollution.

Recovery of nitrogen and phosphorus in wastewater by red mud-modified biochar and its potential application

A large amount of wastewater containing nitrogen, phosphorus, and fluorine produces in the production of phosphate fertilizer. In this study, to simultaneously recover nitrogen and phosphorus from phosphorus-containing wastewater and realize the resource utilization of red mud and rape straw, red mud-modified rape straw biochar (RM/RSBC) was prepared by facile one step, and the physicochemical properties were characterized by Zeta potential, SEM-EDS, BET specific surface area (SSA), FTIR, XRD, and XPS. The adsorption performance and mechanisms of ammonium and phosphate onto RM/RSBC were explored through static, fixed-bed column adsorption, and practical wastewater experiments. The results showed that pH = 3.0 and 8.0 were favorable for the removal of phosphate and ammonium, respectively. The main adsorption mechanisms of ammonium and phosphate were the interaction between ammonium and surface functional groups and surface precipitation, respectively. The removal efficiencies of ammonium and phosphate by fixed-bed column adsorption mainly depended on the addition amount of RM/RSBC, the concentration of ammonium and phosphate, and the flow rate. The results of the germination experiment showed that adding > 0.5 wt% of RM/RSBC loaded with ammonium and phosphate promoted the growth of mung beans. This study shows that RM/RSBC can not only recover ammonium and phosphate in wastewater, but also realize the resource utilization of red mud and rape straw.