Aimal Khan

Synergistic degradation of phenols using peroxymonosulfate activated by CuO-Co3O4@MnO2 nanocatalyst

The development of transition metal based heterogeneous catalysts with efficient reactivity and intensive stability is of great demand in peroxymonosulfate based AOPs in water treatment. Herein, we present a novel approach of creating stable and effective nano-rod catalyst of CuCo@MnO2 with tetragonal structure. A remarkable synergetic effect was found between bi-metallic oxides of Cu and Co: 0.5%Cu-2%Co-MnO2 can efficiently degrade 100% of 30ppm phenol, while 0.5%Cu@MnO2 or 2%Co@MnO2 alone is apparently sluggish for the degradation of organic contaminants. The nanocatalyst retained good stability in recycling tests, during which little leaching of Co and Cu ions can be detected and crystallinity of support α-MnO2 remained unchanged. Mechanism study indicated that SO4- and OH are accounted to participate the degradation, and the generation of radicals is originated from the interaction of CuCo@MnO2 and PMS through metal site with peroxo species bond. The redox cycle among the active metals (M2+↔M3+↔M2+) and Cu enhanced generation of Co(II)-OH complex are critical for the remarkable performance in CuCo@MnO2/PMS system. Both the synergetic acceleration of catalyst activity and instinct mechanism are highly suggestive to the design of heterogeneous catalysts for the degradation of organic contaminants in PMS based advanced oxidation processes.

Highly Efficient Lead Distribution by Magnetic Sewage Sludge Biochar: Sorption Mechanisms and Bench Applications

Highly efficient magnetic sewage sludge biochar (MSSBC) discloses feasible fabrication process with lower production cost, superior adsorption capacity, usage of waste sewage sludge as resource, selected by external magnetic field and exceptional regeneration property. 2gL-1 MSSBC exhibited a high adsorption capacity of 249.00mgg-1 in 200ppmPb(II) and the lead-MSSBC equilibrium was achieved within one hour, owing to the existence of the copious active sites. The adsorption kinetics was well described by the pseudo-second-order model while the adsorption isotherm could be fitted by Langmuir model. Mechanism study demonstrated the adsorption involved electrostatic attraction, ion exchange, inner-sphere complexation and formation of co-precipitates at the surface of MSSBC. Additionally, adsorption performance maintained remarkable in a broad pH window. These outcomes demonstrated the promising waste resource utilization by a feasible approach that turns the solid waste of sewage sludge into biochar adsorbent with auspicious applications in elimination of Pb(II) from wastewater.

Fe-MoS4: An Effective and Stable LDH-Based Adsorbent for Selective Removal of Heavy Metals

It has always been a serious challenge to design efficient, selective, and stable absorbents for heavy-metal removal. Herein, we design layered double hydroxide (LDH)-based Fe-MoS4, a highly efficient adsorbent, for selective removal of heavy metals. We initially synthesized FeMgAl-LDH and then enriched its protective layers with MoS42- anions as efficient binding sites for heavy metals. Various characterization tools, such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray, X-ray photoelectron spectroscopy (XPS), CHN analysis, and inductively coupled plasma analysis, were applied to confirm structural and compositional changes during the synthesis of Fe-MoS4 as final product. The prepared Fe-MoS4 offered excellent attraction for heavy metals, such as Hg2+, Ag+, Pb2+, and Cu2+, and displayed selectivity in the order Hg2+ ∼ Ag+ > Pb2+ > Cu2+ > Cr6+ > As3+ > Ni2+ ∼ Zn2+ ∼ Co2+. The immense capacities of Hg2+, Ag+, and Pb2+ (583, 565, and 346 mg/g, respectively), high distribution coefficient (Kd ∼ 107-108), and fast kinetics place Fe-MoS4 on the top of materials list known for removal of such metals. The sorption kinetics and isothermal studies conducted on Hg2+, Ag+, Pb2+, and Cu2+ suit well pseudo-second-order kinetics and Langmuir model, suggesting monolayer chemisorption mechanism through M-S linkages. XRD and FTIR studies suggested that adsorbed metals could result as coordinated complexes in LDH interlayer region. More interestingly, LDH structure offers protective space for MoS42- anions to avoid oxidation under ambient environments, as confirmed by XPS studies. These features provide Fe-MoS4 with enormous capacity, good reusability, and excellent selectivity even in the presence of huge concentration of common cations.

Synergistic degradation of phenols by bimetallic CuO–Co3O4@γ-Al2O3 catalyst in H2O2/HCO3− system

The development of new catalytic techniques for wastewater treatment has long attracted much attention from industrial and academic communities. However, because of catalyst leaching during degradation, catalysts can be short lived, and therefore expensive, and unsuitable for use in wastewater treatment. In this work, we developed a bimetallic CuO-Co 3 O 4 @γ-Al 2 O 3 catalyst for phenol degradation with bicarbonate-activated H 2 O 2 . The weakly basic environment provided by the bicarbonate buffer greatly suppresses leaching of active Cu and Co metal ions from the catalyst. X-ray diffraction and X-ray photoelectron spectroscopy results showed interactions between Cu and Co ions in the CuO-Co 3 O 4 @γ-Al 2 O 3 catalyst, and these improve the catalytic activity in phenol degradation. Mechanistic studies using different radical scavengers showed that superoxide and hydroxyl radicals both played significant roles in phenol degradation, whereas singlet oxygen was less important.

Bimetallic synergistic degradation of chlorophenols by CuCoOx–LDH catalyst in bicarbonate-activated hydrogen peroxide system

Catalytic wastewater treatment is confronted by varied challenges like catalyst stability and efficiency in aqueous media due to the complex chemistry during organic compound degradation. Herein, we attempt to address this challenge by creating a synergistically stable and active bimetallic CuCoOx–LDH catalyst via facile copper ion hydrothermal impregnation in a CoOx–LDH catalyst. Different instrumental techniques like BET, XRD, FTIR, SEM, XPS and electrochemical studies etc. were conducted to investigate the properties of the catalyst before and after impregnation of copper ions. It was found that the changes in the electrochemistry and redox properties of the CuCoOx–LDH catalyst based on cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) appeared in the form of enhanced activity and excellent stability. In the bicarbonate activation of hydrogen peroxide (BAP) system, the synthesized CuCoOx–LDH catalyst can efficiently degrade 200 ppm 4-chlorophenol (4-CP) with 84% COD and 78% TOC removal in less than 40 minutes, and even 1000 ppm of 4-CP in hours, while the CoOx–LDH and CuOx–LDH catalysts or their physical mixtures are apparently sluggish. This catalyst can also effectively degrade various substituted phenols including 2,4-dichlorophenol (DCP), 2,4,4-trichlorophenol (TCP), 2-chlorophenol (2-CP), phenol, and chlorobenzene with significant COD removal. The findings from fluorescence, scavengers, electron paramagnetic resonance (EPR), XPS, and electrochemical studies suggest collectively the generation of ˙OH, 1O2, and ˙O2− species and that the regeneration of active sites may be part of the degradation process. This approach based on CV, EIS and XPS studies has provided novel knowledge about the intrinsic origins of synergetic acceleration of catalyst activity.

Highly efficient α-Mn2O3@α-MnO2-500 nanocomposite for peroxymonosulfate activation: comprehensive investigation of manganese oxides

In this paper a nanorod α-Mn2O3@α-MnO2-500 nanocomposite demonstrated the highest efficiency and remarkable stability in persulfate activation compared with other manganese oxide based catalysts including α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, α-Mn2O3, Mn3O4, etc. This catalyst was easily fabricated using one spot calcination treatment at 500 °C, and a minimal amount of leached Mn ions was detected during the degradation of organic contaminants. The significant performance in persulfate activation was elucidated from the unique structure and physical-chemical properties of α-Mn2O3@α-MnO2-500. Evidenced by XRD and HRTEM, α-Mn2O3@α-MnO2-500 consisted of a well mixed phase structure of tetragonal α-MnO2 and cubic α-Mn2O3 with high crystalline quality. XPS and the inhibition effect by phosphate confirmed the existence of surface hydroxyl groups (0.926 mmol g−1) on α-Mn2O3@α-MnO2-500, while FTIR, Raman and ionic strength experiments further demonstrated that the formation inner-sphere interaction was the key step in PMS activation. Supported by XPS and CV, the mixed valence states in the α-Mn2O3@α-MnO2-500 nanocomposite exhibited a more effective redox property, which favored electron transfer between Mn species (MnIV ↔ MnIII), and generated SO4˙−, ˙OH and even 1O2 for the degradation of various hydrocarbon contaminants. Also, the activation energy of α-Mn2O3@α-MnO2-500/PMS for phenol degradation was only 24.7 kJ mol−1, much lower than that of α-MnO2 (38.7 kJ mol−1) and α-Mn2O3 (44.9 kJ mol−1). This Mn catalyst with much lower toxicity can be considered as a green approach in environmental remediation.

Towards a better understanding on mercury adsorption by magnetic bio-adsorbents with γ-Fe 2 O 3 from pinewood sawdust derived hydrochar: Influence of atmosphere in heat treatment

Pyrolysis under protective atmosphere was regarded as an indispensable process for the preparation of biomass-based adsorbents to achieve higher surface areas. In this paper, magnetic carbon composites (MCC) that fabricated under air atmosphere showed an adsorption capacity of 167.22 mg/g in 200 ppm Hg(II), which was significantly higher than magnetic biochar (MBC, 31.80 mg/g) that fabricated under traditional nitrogen protection, and this remarkable performance of MCC was consistent in a wide range of pHs. Based on BET, XRD, FTIR, SEM and Boehm titration, MCC was demonstrated with limited surface area (43.29 m2/g) but large amount of surface functional groups comparing with MBC. Additionally, γ-Fe2O3 with a high degree of crystallization was generated in MCC, which led to a better magnetic property and recyclability. Moreover, characterizations, Langmuir isotherm and pseudo-second-order kinetics demonstrated the chemisorption was dominant for MCC in mercury capture, and surface complexation co-precipitate of Hg4Fe8O16C56H40 were also formed.

Facile One-Pot Synthesis of Sustainable Carboxymethyl Chitosan – Sewage Sludge Biochar for Effective Heavy Metal Chelation and Regeneration

In this paper, sewage sludge, a solid waste from wastewater treatment plant, which eagerly requires proper treatment was reused as solid support in the form of sewage sludge biochar, then modified with carboxymethyl chitosan to form a bio-adsorbent. Further, carboxymethyl chitosan coating on sewage sludge biochar improved carboxymethyl chitosans stability in water. The prepared bio-adsorbent revealed a shorter equilibrium time (<60 min) for Pb(II) adsorption and a superior capacity of 594.17 mg g-1 for Hg(II) adsorption, which are so far the best recorded performance achieved for chitosan based adsorbents. Additionally, the adsorbent was highly selective for heavy metal ions and it also presented a good stability and reusability for industrial applications. These outcomes demonstrate waste valorization through a green, facile and one-pot approach that turns the solid waste of sewage sludge into biochar adsorbent with propitious applications in the elimination of heavy metal ions from wastewater.