This paper comparatively investigated the removal efficiency and mechanisms of rice straw biochars prepared under three pyrolytic temperatures for two kinds of tetracycline and quinolone antibiotics (doxycycline and ciprofloxacin). The influencing factors of antibiotic adsorption (including biochar dosage, pH, background electrolytes, humic acid, initial antibiotics concentration, contact time, and temperature) were comprehensively studied. The results suggest that biochars produced at high-temperature [i.e., 700°C (BC700)], have higher adsorption capacity for the two antibiotics than low-temperature (i.e., 300–500°C) biochars (BC300 and BC500). Higher surface area gives rise to greater volume of micropores and mesopores, and higher graphitic surfaces of the BC700 contributed to its higher functionality. The maximum adsorption capacity was found to be in the following order: DOX > CIP. The π-π EDA interaction and hydrogen bonding might be the predominant adsorption mechanisms. Findings in this study highlight the important roles of high-temperature biochars in controlling the contamination of tetracycline and quinolone antibiotics in the environment.
abWith a view to reducing estrogens pollution in aqueous environments, montmorillonite/hydrochar (MMT/ HC) with or without modification by KOH via hydrothermal carbonization process (HTC) were applied to remove 17b-estradiol (E2) and 17a-ethynylestradiol (EE2). The characterizations of MMT/HC indicated that MMT had been successfully attached onto HC surface, which could cause an improvement in the stability of the clay nanoparticles. MMT/HC with 1% KOH (MMT/HC-K1) exhibited excellent adsorption) compared to those of other adsorbents; approximately 2-fold higher than that of HC. Moreover, the adsorption capacity maintained a high level over a wide pH range (2-8). The pseudo-second-order model and Freundlich model exhibited prior fitting performance for adsorption of E2 and EE2. The regenerated MMT/HC-K1 retained over 80% of its initial capacity after four cycles. The adsorption mechanism on MMT/HC-K1 could be explained by hydrophobicity, p-p bond, electrostatic interaction and H-bonding interaction. Overall, MMT/HC-K1 synthesis from two low-cost materials, could be considered as a competitive adsorbent for estrogens removal from aqueous environment, considering its high adsorption capacity and regeneration ability.
BACKGROUND: In this study, manganese oxide (MnO x ) nanoparticle loaded biochar (BC) was applied for doxycycline hydrochloride (DOX) removal from water. Biochar composites were synthesized by either pre-treating biomass using MnCl 2 /KMnO 4 /NaOH (PMBC) or inserting MnO x ultrafine particles after pyrolysis of biomass (AMBC). In complex water environments, the presence of heavy metals may affect the removal of antibiotics. Cu(II) and Cr(VI) were used to study their effect on DOX removal.
RESULTS:The BC loaded with MnO x exhibited superior adsorption properties for DOX. The adsorption capacity of AMBC and PMBC was ≈93 mg/g and 104 mg g −1 , respectively, which was about nine-and ten-fold higher than that of raw BC (11.48 mg g −1 ). The characterization indicated that AMBC and PMBC had better surface structure and more surface functional groups than raw BC. The main mechanisms for DOX adsorption onto PMBC were surface complexation, H-bond, -interaction and electrostatic interaction. DOX removal by PMBC also involved its degradation effect on DOX. Adsorption experiments were carried out with the influence of pH, ionic strength and background electrolyte. The presence of Cu(II) obviously enhanced the DOX adsorption capability through Cu(II) bridging effect, whereas the presence of Cr(VI) significantly inhibited DOX adsorption through competitive adsorption and electrostatic repulsion.
CONCLUSIONS:The results suggested that PMBC could be implemented as a cost-effective and environmentally friendly adsorbent for DOX removal from water. Heavy metal ions can obviously enhance or weaken the adsorption ability of PMBC for DOX.
The cover image, by Zhi‐wei Zeng et al., is based on the Research Article Comparative study of rice husk biochars for aqueous antibiotics removal, DOI: .
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