Surface Water as an Initial Proton Source for the Electrochemical CO Reduction Reaction on Copper Surfaces.

We have employed in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) and density functional theory (DFT) calculations to study the CO reduction reaction (CORR) on Cu single-crystal surfaces under various conditions. Coadsorbed and structure-/potential-dependent surface species, including *CO, Cu-Oad , and Cu-OHad , were identified using electrochemical spectroscopy and isotope labeling. The relative abundance of *OH follows a "volcano" trend with applied potentials in aqueous solutions, which is yet absent in absolute alcoholic solutions. Combined with DFT calculations, we propose that the surface H2 O can serve as a strong proton donor for the first protonation step in both the C1 and C2 pathways of CORR at various applied potentials in alkaline electrolytes, leaving adsorbed *OH on the surface. This work provides fresh insights into the initial protonation steps and identity of key interfacial intermediates formed during CORR on Cu surfaces.

Directing the Architecture of Surface-Clean Cu2O for CO Electroreduction.

Tailoring the morphology of nanocrystals is a promising way to enhance their catalytic performance. In most previous shape-controlled synthesis strategies, surfactants are inevitable due to their capability to stabilize different facets. However, the adsorbed surfactants block the intrinsic active sites of the nanocrystals, reducing their catalytic performance. For now, strategies to control the morphology without surfactants are still limited but necessary. Herein, a facile surfactant-free synthesis method is developed to regulate the morphology of Cu2O nanocrystals (e.g., solid nanocube, concave nanocube, cubic framework, branching nanocube, branching concave nanocube, and branching cubic framework) to enhance the electrocatalytic performance for the conversion of CO to n-propanol. Specifically, the Cu2O branching cubic framework (BCF-Cu2O), which is difficult to fabricate using previous surfactant-free methods, is fabricated by combining the concentration depletion effect and the oxidation etching process. More significantly, the BCF-Cu2O-derived catalyst (BCF) presents the highest n-propanol current density (-0.85 mA cm-2) at -0.45 V versus the reversible hydrogen electrode (VRHE), which is fivefold higher than that of the surfactant-coated Cu2O nanocube-derived catalyst (SFC, -0.17 mA cm-2). In terms of the n-propanol Faradaic efficiency in CO electroreduction, that of the BCF exhibits a 41% increase at -0.45 VRHE as compared with SFC. The high catalytic activity of the BCF that results from the clean surface and the coexistence of Cu(100) and Cu(110) in the lattice is well-supported by density functional theory calculations. Thus, this work presents an important paradigm for the facile fabrication of surface-clean nanocrystals with an enhanced application performance.

Effective adsorption of Direct Red 23 by sludge biochar-based adsorbent: adsorption kinetics, thermodynamics and mechanisms study.

Using solid adsorbents, such as biochar, has been a potential practice to remove the pollutants from water bodies to render the water safer for potential usage. A potential application of sludge biochar-based adsorbent (SBA), obtained by pyrolysis with hydrothermal treatment, was developed to adsorb Direct Red 23 (DR23) from wastewater. The results showed that for the synthesized SBA (0.5 g/L) in the adsorption of DR23 at low concentration (<20 mg/L), the DR23 was totally removed from the aqueous solution. pH had a limited effect on the adsorption, while an increase in temperature was shown to have a large enhancing effect. The adsorption kinetics were best fitted by the pseudo-second-order kinetic model, while the equilibrium data were best fitted by the Langmuir isotherm. A maximum saturation adsorption capacity of SBA of 111.98 mg/g was achieved. SBA could then be regenerated by pyrolysis, and after three cycles, SBA still retained good adsorption ability for DR23, a removal rate exceeding 97% was achieved. Functional groups, pores, π-π bond, and electrostatic interactions are the key to the adsorption mechanisms. The results proved that SBA would be a promising material in the application of removing dyes in printing and dyeing wastewater.

Heavy metal stabilization and improved biochar generation via pyrolysis of hydrothermally treated sewage sludge with antibiotic mycelial residue.

Hydrothermally treated sewage sludge was pyrolyzed at temperatures of 300, 500, and 700 °C with antibiotic mycelial residue addition ratios of 0, 10, 25, and 50 wt%. The results showed that co-pyrolysis could obviously improve biochar properties. Specifically, adding antibiotic mycelial residue increased the aromaticity and raised the higher heating value of the biochar, which indicates its better potential as fuel. The enrichment in functional groups improved the surface properties of biochar, indicating its better applicability. Additionally, the heavy metal concentrations in biochar were diluted by adding antibiotic mycelial residue, which led to lower toxic inputs to the environment. Moreover, heavy metals were transformed to more stable fractions after co-pyrolysis. A higher pyrolysis temperature and greater antibiotic mycelial residue amounts led to better immobilization of heavy metals, thus preventing their leaching to the environment. This work proposes a promising technique for the synergetic treatment of sewage sludge and antibiotic mycelial residue for improved biochar formation.

Chemical speciation and distribution of potentially toxic elements in soilless cultivation of cucumber with sewage sludge biochar addition.

Potentially toxic elements in municipal sewage sludge can be effectively immobilized during biochar production via pyrolysis. However, the bioavailability of these elements when biochar is applied in soilless cultivation to improve substrate quality has yet to be sufficiently established. In this study, we investigated the chemical speciation and cucumber plant uptake of potentially toxic elements in soilless cultivation when the growth substrate was amended with sewage sludge biochar (0, 5, 10, 15, and 20 wt%). It was found that the addition of 10 wt% biochar was optimal with respect to obtaining a high cucumber biomass and achieving low environmental risk considering the occurrence of hormesis. When the substrate was amended with 10 wt% biochar, cucumber fruit contained lower concentrations of As, Cr, and Zn and smaller bioavailable fractions of As, Cd, Cr, Ni, Cu, and Zn compared with the fruit of control plants, thereby meeting national safety requirements (standard GB 2762-2012, China). Most of the As and Cd taken up by cucumbers accumulated in the leaves and fruit, whereas Cr was found primarily in the roots, and most Ni, Cu, and Zn was detected in the fruit. Importantly, only small proportions of the potentially toxic elements in biochar were taken up by cucumber plants (As: 0.0075%; Cd: 0.038%; Ni: 0.0064%; Cu: 0.0016%; and Zn: 0.0015%). Given that the As, Cd, Ni, and Zn speciation in sewage sludge biochar was effectively immobilized after cultivation, the findings of this study indicate that sewage sludge biochar is a suitable substrate amendment in terms of the risk posed by potentially toxic elements.

Ciprofloxacin adsorption by biochar derived from co-pyrolysis of sewage sludge and bamboo waste.

Antibiotics residues in aqueous environment and sewage sludge accumulation have become serious environmental issues. The aim of this study is to investigate the potential of ciprofloxacin (CIP) removal by sludge-based biochar prepared from co-pyrolysis of sewage sludge and bamboo waste (BW). The stability and environmental risk of heavy metals (HMs) in the biochar were further investigated to evaluate potential risks for biochar utilization. Results showed that BW was an outstanding additive to prepare co-pyrolyzed biochar from sludge. A higher CIP removal rate (95%) of BW-sludge biochar (SBC) was obtained under initial CIP concentration of 10 mg/L, and its maximum adsorption capacity was 62.48 mg/g which was calculated from the Langmuir model. The pseudo-second-order and Freundlich model also well fit the CIP adsorption process, indicating a chemical and multilayer adsorption of CIP on a heterogeneous surface of biochar. Adsorption mechanism analysis indicated that the diverse functional groups and Fe species in biochar probably were the dominant factors in the adsorption of CIP. The π-π interaction, H-bond, ion exchange, and Fe-complexation might be the main interactions between the functional species and CIP molecules. Besides, HMs, especially the Cr, Cd, and As, were well immobilized in SBC compared with pure sludge biochar. This work suggested that sludge-based biochar, especially the co-pyrolyzed SBC, could be a potential adsorbent for CIP removal from aqueous solutions.

Dewaterability enhancement and heavy metals immobilization by pig manure biochar addition during hydrothermal treatment of sewage sludge.

Hydrothermal treatment (HTT) of sewage sludge (SS) with pig manure biochar (PMB) addition at 160-200 °C was conducted in this study. The effects of PMB addition on the dewaterability of SS and the speciation evolution, leaching toxicity, and potential ecological risk of heavy metals were investigated. The results showed that the solid contents of the filter cakes after adding PMB increased from 20.24%, 24.03%, and 28.69% to 21.57%, 27.69%, and 32.91% at 160, 180, and 200 °C, respectively, compared with traditional HTT of SS. Furthermore, PMB could reduce the bioavailable fractions of Cr, Ni, As, and Cd in the filter cakes obtained at 160 and 180 °C compared with the theoretical value. The leaching toxicity of heavy metals in the filter cakes after adding PMB decreased significantly at 160 and 180 °C and the potential ecological risk index (RI) declined from 62.13 and 44.83 to 55.93 and 42.11, respectively. The obtained filter cake had low potential ecological risk when used in the environment. The mechanisms on the improvement of the dewaterability and heavy metals immobilization were related that PMB acted as the skeleton builder providing the outflow path for free water and implanting heavy metals into SS structure. And the optimal results were obtained at 180 °C during HTT of SS with PMB addition. This work provides a novel and effective method for the treatment of SS.

The synthesis of heterogeneous Fenton-like catalyst using sewage sludge biochar and its application for ciprofloxacin degradation.

The terminal utilization of sewage sludge biochar (SSB) is nonnegligible and significant for sewage sludge (SS) treatment by pyrolysis. In this paper, a novel low-cost recyclable sludge biochar catalyst (SBC) that can be employed as a heterogeneous Fenton-like catalyst was prepared using SSB from SS pyrolysis in a pilot-scale platform for ciprofloxacin (CIP) degradation. The fabricated SBC was analyzed to characterize its surface micrographs, pore structures, and chemical composition. The catalytic effect of SBC on CIP degradation was also explored to determine the feasibility of using SBC to remove aquatic organic contaminants, and its degradation mechanism and pathway were also discussed. SBC can effectively remove CIP by adsorption and enhance the degradation of CIP by its catalytic effect. >80% of the CIP was removed at pH 4.0, and the antimicrobial activity of the resulting products was considerably reduced. The possible degradation mechanism is associated with the synergetic effect of adsorption and oxidative degradation. Oxidizing radical was generated from H2O2 by the activation of Fe2+ and Fe3+, which released from SBC, and HO was the dominant radical in CIP degradation. Piperazine ring cleavage, pyridine cleavage and hydroxylation, F/OH substitution, and defluorination were the dominant degradation pathways. The heavy metal risk assessment showed that SBC exhibits low environmental and ecological risk. This study provides a prospective method for high-value utilization of SSB and a novel and potentially low-cost catalyst for CIP removal from aqueous environments, which is significant for the terminal disposal of SS.

Study of ciprofloxacin removal by biochar obtained from used tea leaves.

In this study, used tea leaves (UTLs) were pyrolyzed to obtain used tea-leaf biochar (UTC), and then the UTC was used as an adsorbent to remove ciprofloxacin (CIP) from aqueous solutions. Batch experiments were conducted to investigate the CIP adsorption performance and mechanism. The results showed that the CIP-adsorbing ability first increased and then declined as the UTC pyrolysis temperature increased. The UTC obtained at 450°C presented excellent CIP-absorbing ability at pH6 and 40°C. The maximum monolayer adsorption capacity was 238.10mg/g based on the Langmuir isotherm model. The pseudo-second-order kinetic equation agreed well with the CIP adsorption process, which was controlled by both external boundary layer diffusion and intra-particle diffusion. The characterization analysis revealed that the OH groups, CC bonds of aromatic rings, CH groups in aromatic rings and phenolic CO bonds play vital roles in the CIP adsorption process, and that the NC, NO, OCO and COH groups of UTC were consumed in large quantities. π-π interactions, hydrogen bonding and electrostatic attraction are inferred as the main adsorption mechanisms. The present work provides not only a feasible and promising approach for UTLs utilization but also a potential adsorbent material for removing high concentrations of CIP from aqueous solutions.

Immobilization of heavy metals in ceramsite produced from sewage sludge biochar.

Ceramsite was prepared from sewage sludge biochar (SSB). The migration, speciation evolution, leaching toxicity, and potential environmental risk of heavy metals (HMs) in sludge biochar ceramsite (SBC) were investigated. The characteristics of the SBC met the requirements for Chinese lightweight aggregate standards (GB/T 1743.1-2010 and JT/T 770-2009) and the heavy metals (HMs: Cu, Zn, Cr, Pb, and Cd) were well immobilized in the SBC. The leaching percentages of the HMs in SBC were remarkably reduced, in particular after preheating at 400°C and sintering at 1100°C. The leaching percentages of Cu, Zn, Cr, Cd, and Pb decreased from (19.099, 18.009, 0.010, 3.952, and 0.379) % to (2.122, 4.102, 0.002, 1.738, and 0.323) %, respectively. The RAC values of the HMs in SBC were all lower than 1%, and the risk index (RI) suggested that the SBC had no HMs contamination and very low potential ecological risk when used in the environment. Furthermore, the HM-immobilization mechanisms were mainly related to the formation of new crystal phases (silicate and phosphate minerals) by incorporation of HMs, and to vitrification and encapsulation with low concentration of HMs on the surface. This work provides a useful method for large-scale reuse of SSB with very low leaching toxicity and low potential ecological risk of HMs.

[Preparation of Adsorption Ceramsite Derived from Sludge Biochar].

Adsorption ceramsite (SKC) was prepared with biochar (BC) derived from municipal sludge and kaolin (KL) based on the optimized processing parameters to adsorb ciprofloxacin (CIP) in aqueous solutions. The CIP adsorption mechanism of SKC was investigated by adsorption kinetics and isotherm adsorption models, combined with the analysis of microstructure, pore structure, phase composition, and zeta potential. Furthermore, the heavy metal leaching toxicity was assessed using the toxicity characteristic leaching procedure (TCLP) method. The results showed that SKC, with 60% BC and 40% KL calcining at 1,050℃ for 5 min, showed an outstanding removal efficiency of CIP (65.34%). The pseudo-second-order equation agreed with the adsorption behavior and the Freundlich model described the adsorption process well. The adsorption process was a multilayer adsorption controlled by physical and chemical reactions. The leaching concentration of heavy metals, trapped by the mineral phases in SKC was much lower than that in BC, indicating low ecotoxicological risk. SKC possessed the ability to adsorb CIP with its developed porosity and characteristic mineralogical phases, including silicon aluminum oxide and iron oxide. This work provides a low-cost recyclable sorbing material to remove high concentration CIP from wastewater and offers a new idea for the large-scale safe use of BC.