Selenium and nitrogen co-doped biochar as a new metal-free catalyst for adsorption of phenol and activation of peroxymonosulfate: Elucidating the enhanced catalytic performance and stability.

Coupling of adsorption and advanced oxidation processes triggered by metal-free carbocatalysts is an appealing wastewater purification scheme. However, its practical application is challenging due to the unsatisfactory stability of conventional heteroatom-doped systems. Herein, we innovatively developed a simple and scalable biochemical strategy to synthesize selenium and nitrogen co-doped biochar (Se/N-BC) as a bifunctional catalyst of adsorption-oxidation. The Se/N-BC displays the highest efficiency of phenol (PE) degradation (99.2% of PE was removed within 5 min) with the lowest dosage of catalyst (0.1 g L-1) and peroxymonosulfate (PMS, 0.4 g L-1). More importantly, the Se/N-BC is not only universal in a wide pH range of 3.0-11.0 and complex ionic environment, but also possesses an excellent cycling stability. The Se/N co-doping induces a rapid cycle of adsorption-degradation for PE. The Se/N-BC acts as an "electron transfer bridge", guiding rapid electron transfer from PE to PMS to achieve high-efficient degradation. The Se/N co-doping facilitates the formation of graphitic N and unlocks the potential of adjacent C sites for PMS activation, consequently boost oxidation efficiency. In addition, the oxidation of catalyst is prevented due to the antioxidant properties of Se, which has been a primary concern either to regenerate adsorbate or to enhance degradation performance.

Biodeposited Nano-CdS Drives the In Situ Growth of Highly Dispersed Sulfide Nanoparticles during Pyrolysis for Enhanced Oxygen Evolution Reaction.

A novel, efficient, and stable graphene-based composite oxygen evolution reaction (OER) catalyst, BG@Ni/Ni3S2, was designed via high-specificity, low-cost biosynthesis and efficient electrostatic self-assembly. In the synthetic process, bacterial cells containing biodeposited CdS nanocrystals, graphene oxide (GO), and Ni2+ ions are assembled into a sandwich-type hybrid precursor. The nanosized sulfur source drives in situ sulfidation during pyrolysis, which induces the uniform formation and growth of Ni/Ni3S2 composite nanoparticles (NPs) on the graphene substrate. Benefiting from the high specific surface area and uniform distribution of NPs, the catalyst has a large number of exposed active sites and exhibits rapid mass transfer. In addition, the skeleton composed of a conductive carbon matrix and metallic Ni-Ni network ensures the excellent electron transfer during the OER, and the synergistic effect of Ni0 and Ni3S2 further optimizes the electronic structure and accelerates the OER kinetics. The dominant catalytic sites at the nanointerface between Ni0 and Ni3S2 provide favorable thermodynamic conditions for the adsorption of OER intermediates. As a result, BG@Ni/Ni3S2 exhibits efficient catalytic performance for the OER: the overpotential and Tafel slope are only 320 mV at 100 mA cm-2 and 41 mV dec-1, respectively. This work provides a novel understanding of the intrinsic activity of transition metal sulfide composites and a biological-based design for OER catalysts.

Exceptional adsorption of arsenic by zirconium metal-organic frameworks: Engineering exploration and mechanism insight.

Highly stable zirconium metal-organic frameworks (UiO-66 and UiO-66(NH2)) had been synthesized and investigated to remove arsenic (As) from contaminated water. The As(III, V) removal performance was studied by batch experiments and adsorption kinetics. At the pH of 9.2 ±â€¯0.1, UiO-66 had exceptional removal capacities of 205.0 and 68.21 mg/g for As(III) and As(V), respectively. The As removal processes were exothermic and verified as chemisorption reactions according to the calculation of Gibbs free energy and Dubinin-Radushkevich (D-R) isotherm model. Fixed-bed reactor removal experiments indicated that the number of effective treatment volumes reached 2270 and 1775 BVs for As(III) and As(V), respectively, until the most stringent As regulation level of 10 µg/L (initial As concentration at 100 µg/L) was reached. FTIR and XPS study indicated that ZrO bonds of zirconium metal-organic frameworks played a vital role in As adsorption. XANES revealed the As adsorption on UiO-66 without the change of oxidation state. More intriguingly, EXAFS spectra demonstrated the main formation of bidentate mononuclear complexes for As(V), and bidentate binuclear complexes for As(III) on the hexanuclear Zr cluster of UiO-66. The advantages of nontoxicity, high stability, high As adsorption capacity, low-cost and easy availability confirm the highly promising application of zirconium metal-organic frameworks in As-contaminated wastewater remediation.

Development of an anion imprinted polymer for high and selective removal of arsenite from wastewater.

A novel cyclic functional monomer (CFM) was used to develop an As(III)-ion imprinted polymer (As-IIP). CFM possesses a positively charged imidazolium moiety and its specific cyclic size matches that of As(III). Batch adsorption experiments showed that the As-IIP has a maximum As(III) adsorption capacity of 55 mg/g, while that of the control polymer (CP) is only 25 mg As(III)/g. Adsorption isotherms for As(III) agree with the Langmuir model, suggesting monolayer adsorption. Kinetic studies showed that the adsorption process followed pseudo-second-order kinetics. The relative selectivity coefficients of As-IIP compared to CP for Cl-/H2AsO3-, SO42-/H2AsO3-, HPO42-/H2AsO3-, NO3-/H2AsO3-, and Mo7O246-/H2AsO3- are 1.03, 1.95, 2.55, 1.52 and 2.51, respectively. The removal efficiency of As-IIP for As(III) in actual industrial wastewater was nearly 100%, which confirms that As-IIP has a high adsorption capacity as well as selectivity for the removal of As(III) from wastewater.

New insight on the adsorption capacity of metallogels for antimonite and antimonate removal: From experimental to theoretical study.

Development of high capacity material for antimonite (Sb(III)) and antimonate (Sb(V)) removal is the key to solving water antimony contamination. Three-dimensional Cu(II)-specific metallogels (Cu-MG), which are considered to have high density adsorption sites for antimony (Sb), were first applied to adsorb Sb(III) and Sb(V). Batch assays resulted in adsorption capacities of Cu-MG for Sb(III) and Sb(V) at 102.4 mg/g and 264.1 mg/g, respectively. In addition, the adsorption capacity for Sb(III) was up to 225.7 mg/g using in situ oxidation. Kinetic assays resulted in more than 90% removal of Sb in 30 min. X-ray photoelectron spectroscopy (XPS) revealed the adsorption of Sb depended mainly on coordination interactions of vacant orbitals of the Cu atom with the lone-pairs of the O atom of Sb(OH)3 or Sb(OH)6-. Adsorption energy based on density functional theory (DFT) confirmed that Sb(III) adsorbed as a single layer whereas Sb(V) adsorbed as a multi-layer. These findings are consistent with experimental results. In addition, DFT calculations revealed that the Cu-MG theoretical capacity for Sb(V) adsorption is higher than for Sb(III). Cu-MG is a new and promising class of adsorbents for the removal of Sb(III) and Sb(V) from contaminated water.