Porous-carbon/manganese composite catalyst transformed from waste biomass as peroxymonosulfate activator for carbamazepine degradation.

Activation of peroxymonosulfate (PMS) with solid catalysts for organic pharmaceutical degradation still faces challenge due to the demand of inexpensive catalysts. In this study, manganese-oxidizing microalgae (MOM) and its associated biogenic manganese oxides (BMO) were employed to prepare biomass-transformed porous-carbon/manganese (B-PC/Mn) catalyst through high-temperature calcination (850 °C). Remarkably, 100 % of carbamazepine (CBZ) was degraded within 30 min in the B-PC/Mn/PMS system. The degradation kinetic constant was 0.1718 min-1, which was 44.0 times higher than that of the biomass-transformed porous carbon mixed with MnOx activated PMS system. 1O2 was generated in the B-PC/Mn/PMS system, which is responsible for CBZ degradation. The MOM-BMO-associated structure greatly increased the specific surface areas and the contents of the C = O and pyrrolic-N groups, which facilitated PMS activation. The structure also induced the generation of Mn5C2, which exhibited a strong adsorption towards PMS. This study provides a novel strategy for preparing catalysts by using waste biomass.

The Enhanced Performance of NiCuOOH/NiCu(OH)2 Electrode Using Pre-Conversion Treatment for the Electrochemical Oxidation of Ammonia.

Electrochemical oxidation of ammonia is an attractive process for wastewater treatment, hydrogen production, and ammonia fuel cells. However, the sluggish kinetics of the anode reaction has limited its applications, leading to a high demand for novel electrocatalysts. Herein, the electrode with the in situ growth of NiCu(OH)2 was partially transformed into the NiCuOOH phase by a pre-treatment using highly oxidative solutions. As revealed by SEM, XPS, and electrochemical analysis, such a strategy maintained the 3D structure, while inducing more active sites before the in situ generation of oxyhydroxide sites during the electrochemical reaction. The optimized NiCuOOH-1 sample exhibited the current density of 6.06 mA cm-2 at 0.5 V, which is 1.67 times higher than that of NiCu(OH)2 (3.63 mA cm-2). Moreover, the sample with a higher crystalline degree of the NiCuOOH phase exhibited lower performance, demonstrating the importance of a moderate treatment condition. In addition, the NiCuOOH-1 sample presented low selectivity (<20%) towards NO2- and stable activity during the long-term operation. The findings of this study would provide valuable insights into the development of transition metal electrocatalysts for ammonia oxidation.

Synthesis of a Novel Dithiocarbamate Surfactant Derivative Adsorbent for Efficient Removal of Heavy Metal Ions.

In this work, a novel heavy metal chelating agent (DTC-SDS) containing dithiocarbamate (DTC) was synthesized using sodium dodecyl sulfate (SDS), formaldehyde, and carbon disulfide. DTC-SDS has excellent trapping performance under pH 1-7 and initial concentrations 100-500 mg/L. With the increase in adsorbent dose, the adsorption amount of DTC-SDS increases and then decreases, and the optimized dosage of DTC-SDS is 0.02 g. The DTC-SDS adsorbent exhibits superior adsorption capacity (191.01, 111.7, and 79.14 mg/g) and high removal rates (97.99%, 98.48%, and 99.91%) for Mn2+, Zn2+, and Pb2+ respectively, in wastewater. Such remarkable adsorption performance could be attributed to the strong trapping effect on heavy metal ions by the C-S bond of DTC-SDS. The liquid adsorbent was in full contact with heavy metal ions, which further enhanced the complexation of heavy metal ions. The adsorption isothermal model showed that the adsorption process was typical of Langmuir monomolecular layer adsorption. Kinetic studies showed that the pseudo-second-order kinetic model fits the experimental adsorption data better than the pseudo-first-order kinetic model. In the ternary metal species system (Mn2+, Zn2+, and Pb2+), DTC-SDS preferentially adsorbed Pb2+ due to its highest covalent index. The main controlling step is the chemical interaction between the active groups of DTC-SDS and the heavy metal ions. This work provides valuable insights into the adsorption of heavy metal ions onto dithiocarbamate, which could guide the development of other heavy metal chelating agents and be beneficial for developing novel treatments of wastewater contaminated with heavy metals.

Long-Term Performance of Nitrogen Removal and Microbial Analysis in an Anammox MBBR Reactor with Internal Circulation to Provide Low Concentration DO.

The anammox process is considered as a revolutionary new denitrification technology. In this study, the anammox process was started in a single-stage moving bed biofilm reactor (MBBR) and the mechanism of excess removal of ammonia nitrogen was studied. At stage I (day 0-51), anammox bacteria (AnAOB) was enriched by feeding synthetic sewage without adding organic carbon. The removal rate of ammonia nitrogen was maintained at about 54% and the removal rate of total inorganic nitrogen was maintained at about 62%. At stage II (day 52-91), internal circulation was added into the MBBR. After adding internal circulation, the ammonium removal efficiency reached about 96% (at day 56) and the total nitrogen removal efficiency reached about 86%. At day 90, the biofilm sample was drowned out for high-throughput sequencing. The results showed that the relative abundance of AnAOB was 23.23%. The dominant anammox genus was Candidatus Brocadia. The relative abundance of Nitrosomonas (ammonia oxidizing bacteria, AOB) was 0.63%. The excess ammonia nitrogen was removed by AOB and AnAOB through the partial nitrification and anammox (PNA) process.

Combined Process of Biogenic Manganese Oxide and Manganese-Oxidizing Microalgae for Improved Diclofenac Removal Performance: Two Different Kinds of Synergistic Effects.

Biogenic manganese oxides (Bio-MnOx) have attracted considerable attention for removing pharmaceutical contaminants (PhCs) due to their high oxidation capacity and environmental friendliness. Mn-oxidizing microalgae (MnOMs) generate Bio-MnOx with low energy and organic nutrients input and degrade PhCs. The combined process of MnOMs and Bio-MnOx exhibits good prospects for PhCs removal. However, the synergistic effects of MnOMs and Bio-MnOx in PhCs removal are still unclear. The performance of MnOMs/Bio-MnOx towards diclofenac (DCF) removal was evaluated, and the mechanism was revealed. Our results showed that the Bio-MnOx produced by MnOMs were amorphous nanoparticles, and these MnOMs have a good Mn2+ tolerance and oxidation efficiency (80-90%) when the Mn2+ concentration is below 1.00 mmol/L. MnOMs/Bio-MnOx significantly promotes DCF (1 mg/L) removal rate between 0.167 ± 0.008 mg/L·d (by MnOMs alone) and 0.125 ± 0.024 mg/L·d (by Bio-MnOx alone) to 0.250 ± 0.016 mg/L·d. The superior performance of MnOMs/Bio-MnOx could be attributed to the continuous Bio-MnOx regeneration and the sharing of DCF degradation intermediates between Bio-MnOx and MnOMs. Additionally, the pathways of DCF degradation by Bio-MnOx and MnOMs were proposed. This work could shed light on the synergistic effects of MnOMs and Bio-MnOx in PhCs removal and guide the development of MnOMs/Bio-MnOx processes for removing DCF or other PhCs from wastewater.

N-Doped Graphene as an Efficient Metal-Free Electrocatalyst for Indirect Nitrate Reduction Reaction.

N-doped graphene samples with different N species contents were prepared by a two-step synthesis method and evaluated as electrocatalysts for the nitrate reduction reaction (NORR) for the first time. In an acidic solution with a saturated calomel electrode as reference, the pyridinic-N dominant sample (NGR2) had an onset of 0.932 V and a half-wave potential of 0.833 V, showing the superior activity towards the NORR compared to the pyrrolic-N dominant N-doped graphene (onset potential: 0.850 V, half-wave potential: 0.732 V) and the pure graphene (onset potential: 0.698 V, half-wave potential: 0.506 V). N doping could significantly boost the NORR performance of N-doped graphene, especially the contribution of pyridinic-N. Density functional theory calculation revealed the pyridinic-N facilitated the desorption of NO, which was kinetically involved in the process of the NORR. The findings of this work would be valuable for the development of metal-free NORR electrocatalysts.

A new insight into the mechanism of carbamazepine oxidation by MnO2: Crystalline structure versus Mn(III).

Mn(III) has been regarded as the origin of oxidative reactivity of MnO2 recently, however this remains controvertible. Herein, carbamazepine (CBZ), a typical refractory pharmaceutical, was treated by δ-, α-, ß-, and γ-MnO2 and the role of Mn(III) was investigated. After the removal of Mn(III) by pyrophosphate washing, the δ-MnO2 exhibited a higher kinetics rate (0.180 min-1) than the sample before washing (0.075 min-1). Dissolved Mn(III) in the forms of acetate-complex Mn(III), newly acid-dissolved Mn(III) from MnO2 solid, and in-situ generated Mn(III) showed negligible oxidative reactivity towards the oxidation of CBZ. These evidenced that Mn(III) did not play a critical role in the oxidation of CBZ. The oxidative reactivity of MnO2 with different structures for the oxidation of CBZ followed the order: δ-MnO2 >> > α-MnO2 ≈ Î³-MnO2 > ß-MnO2. Density functional theory calculations suggested that the crystalline plane of δ-MnO2 significantly contributed to the oxidation of CBZ, thus leading to the superior performance of δ-MnO2. A new surface reaction dominated mechanism was proposed, which implies that the oxidative reactivity of MnO2 may not result from Mn(III) as previously believed. These findings could shed light on the understanding of MnO2-involved oxidation in water treatment and natural processes.

Cobalt Nanoparticles Encapsulated in Porous Carbons Derived from Core-Shell ZIF67@ZIF8 as Efficient Electrocatalysts for Oxygen Evolution Reaction.

The synthesis of electrocatalysts consisting of selectively functionalized parts is an effective strategy to prepare nonprecious electrocatalysts with excellent performance for oxygen evolution reaction (OER). Herein, we synthesized core-shell structured ZIF67@ZIF8 and converted it into Co decorated porous carbons (CS-Co/Cs) consisting of the ZIF67 derived uniformly dispersed Co nanoparticles encapsulated in graphitic carbon as cores and the ZIF8 derived porous carbon as shells. Compared to individual ZIF67 derived samples (Co/Cs), the unique structure of CS-Co/Cs leads to the larger surface area and more hydrophilic surface, both of which facilitate the mass transfer, contributing to the enhanced OER performance. The optimized CS-Co/C sample presents the low overpotential of 290 mV to deliver 10 mA cm-2 toward OER in 1 M KOH, which is among the best of the reported nonprecious OER electrocatalysts. The CS-Co/C exhibits no obvious current attenuation at 1.53 V for 30 000 s, demonstrating its robust stability.

Nano-cubic structured titanium nitride particle films as cathodes for the effective electrocatalytic debromination of BDE-47.

An energetic TiN cathode was fabricated for effective electrocatalytic debromination of 2,2',4,4'-tetrabromodiphenyl ethers (BDE-47); this was achieved by placing Ti foils in an aqueous suspension of TiN nanoparticles, then drying the system at 50 °C for 12 h. TEM and SEM characterization showed that the TiN nanoparticles-whose average size was approximately 50 nm-were ideal nano-cubic structures and distributed uniformly on the Ti substrate. When applied as a cathode in cyclic voltammetry measurements, the TiN electrode exhibited stable electrochemical performance over 20 cycles, in the ∼1-10 pH range. The overpotential of the TiN cathode for electrochemical reduction of water (the main side reaction during the electrocatalytic reduction of pollutants in aqueous solution) was determined as 0.54 V, which was much higher than the values for either a Pt wafer (0.12 V), or a Pt film (0.07 V). The TiN electrodes displayed superior electrocatalytic activity for the electrocatalytic debromination of BDE-47. The kinetic constant of BDE-47 degradation on TiN cathode is 0.65 h(-1), which was 2, 4 and 17 times as much as those on Pt film, Pt wafer and graphite cathodes, respectively. A pathway was proposed for the degradation of BDE-47, based on measurements of the intermediate products resulting from the removal of BDE-47 by GC-MS.