Efficient removal of antimonate and antimonite by a novel lanthanum-manganese binary oxide: Performance and mechanism.

Antimony is a highly toxic pollutant and its removal from water gains increasing attention. To effectively remove both Sb(III) and Sb(V), a novel lanthanum-manganese binary oxide (L1M2BO) adsorbent was synthesized by a simple oxidation coupled with precipitation method. The as-prepared L1M2BO was detailedly characterized by the XRD, SEM, TEM, BET, FTIR and XPS techniques. It is amorphous and irregular in shape, with a particle size of 50-100 nm and a specific surface area of 180.4 m2/g. A remarkable synergistic effect between the lanthanum hydroxide and Mn oxide in improving antimony adsorption is shown. The maximum adsorption capacities of Sb(III) and Sb(V) are 364.6 mg/g and 131.1 mg/g at pH 7.0, respectively, which outcompete most of reported adsorbents. The adsorption behaviors of antimony fitted well the pseudo-second-order kinetic and Freundlich models. The adsorption mechanism of Sb(V) involves mainly the replacement of surface metal hydroxyl and forming inner-sphere complex. While the Sb(III) removal is a more complicated process, containing both Sb(III) adsorption and oxidation to Sb(V). Furthermore, the spent L1M2BO sorbent can be regenerated and reused. The L1M2BO could be used as an attractive adsorbent for antimony removal, owing to its easily fabrication, high effectiveness and reusability.

The enhanced removal of arsenite from water by double-shell CuOx@MnOy hollow spheres (DCMHS): behavior and mechanisms.

To facilitate removing As(III) from water through an "oxidation-adsorption" process, the double-shell CuOx@MnOy hollow spheres (DCMHS) have been fabricated via a two-step co-precipitation route combined with the soft-template method. The surface characterization results showed that Mn oxides were formed without segregation and uniformly distributed on the surface of CuOx hollow spheres. DCMHS could achieve outstanding performance to remove As(III) with an As maximum adsorption capacity of 32.15 mg/g. Meanwhile, the kinetics results illustrated that the oxidative activity of DCMHS was strengthened due to its specific structure, and part of As(III) was converted to As(V) during the adsorption process. Also, air aeration could further enhance As(III) oxidation and thus improving As removal. The As(III) removal performance could be maintained under neutral and weak alkaline conditions. Phosphate, silicate, and carbonate anions could depress the removal performance, while chloride ions and sulfate anions barely influenced As removal. Moreover, DCMHS could be regenerated using NaOH and KMnO4 solutions without breaking the hollow sphere structure. Based on the spectroscopic analysis results, As(III) molecules were converted to As(V) via two pathways, including the oxidation by Mn oxides or superoxide radicals. The Cu-Mn synergistic effect could not only enhance the oxidative activity of Mn oxides but also produce superoxide radicals via the activation of surface-adsorbed oxygen molecules. Afterwards, the newly formed As(V) could be attached to the hydroxyl groups through surface complexation. Therefore, this work has provided insights into the morphology design of Mn-oxide-containing adsorbents and supplemented the interface reaction mechanisms for enhancing As(III) removal.

The removal of tetracycline, oxytetracycline, and chlortetracycline by manganese oxide-doped copper oxide: the behaviors and insights of Cu-Mn combination for enhancing antibiotics removal.

Adsorption process is suitable to the advanced treatment of tetracycline antibiotics (TCs; including tetracycline (TTC), oxytetracycline (OTC), and chlortetracycline (CTC)) in poultry wastewater. In this research, Mn oxide-doped Cu oxide (MODCO) was synthesized and used for the removal of TTC, OTC, and CTC. According to the XRD and SEM analysis results, MODCO has an amorphous crystal structure and is formed by the aggregation of nano-sized particles with a uniform distribution of Cu and Mn elements. In addition, MODCO has a BET surface area of 67.7 m2/g and a pHIEP value of 7.8. The results of batch experiments illustrated that the reaction rates for the removal of three TCs were in the order of OTC > CTC > TTC. In addition, the theoretical maximum amounts of TTC, OTC, and CTC adsorbed on MODCO were determined to be 2.90 mmol/g, 4.15 mmol/g, and 2.20 mmol/g via the Langmuir model, respectively. The optimal removal performances of TCs were achieved in the pH range of 6~9, and the coexistence of anions posed an unnoticeable effect on the removal efficiencies. The spectroscopic analysis results demonstrated that the removal mechanism of TCs was mainly attributed to surface complexation. Furthermore, a part of TCs may be decomposed by Mn oxides during the removal process according to the UV spectrogram results. Overall, MODCO has exhibited a great potential for the removal of TCs from aqueous solution.