Chenming Liu

KOH self-templating synthesis of three-dimensional hierarchical porous carbon materials for high performance supercapacitors

We report a KOH self-templating synthesis of three-dimensional hierarchical porous carbon using resol as the precursor and KOH as both the template and activating agent. The resulting resol-derived porous carbon (RPC) exhibits a high surface area (up to 2700 m2 g−1) and well-interconnected macropores with micropores and mesopores decorated on the carbon walls. Consequently, the RPC shows low internal resistance, high specific capacitance, good rate capability and excellent cycling stability in 6 M KOH as a supercapacitor electrode. Because of its easy fabrication and low cost, it offers a good alternative method for synthesis of carbon electrodes for energy-storage devices such as Li-ion batteries, fuel cells and supercapacitors.

A combination of electro-enzymatic catalysis and electrocoagulation for the removal of endocrine disrupting chemicals from water.

We in this study investigated a novel electrochemical approach combining electro-enzyme and electrocoagulation to precipitate bisphenol A (BPA) from water containing humic acid (HA). Horseradish peroxidase was immobilized on the graphite felt of Ti electrode as HRP-GF/Ti cathode, with aluminum plate anode establishing a pair of working electrodes. BPA was 100% removed and the reduction of total organic carbon (TOC) reached 95.1% after 20-min sequencing treatment with the current density of 2.3 mA/cm(2). Real wastewater (TOC=28.76 mg/L, BPA=4.1 μg/L) also can achieve 94% BPA removal and 52% TOC reduction after sequencing treatment. Additionally, coupled electro-system with continuous flow only required energy of 0.016 kWh/m(3) to achieve simultaneous 90% BPA and 85% TOC removal. As indicated in the time-of-flight mass spectrometry and FTIR spectra, the electro-enzymatic process not only oxidized BPA into dimer and BPA-3,4-quinone, but also greatly altered the chemical and structural features of HA, where hydrophilic moieties (phenolic and alcohols) transformed into hydrophobic forms (ethers, quinone and aliphatic). These polymerized products were effectively separated from aquous solution during anodic electrocoagulation, leading to significant removal of BPA and TOC. Thus, the coupled process may provide a faster and less energy strategy to control certain emerging contaminants in water/wastewater treatment.

A Highly Sensitive and Selective Hydrogen Peroxide Biosensor Based on Gold Nanoparticles and Three-Dimensional Porous Carbonized Chicken Eggshell Membrane

A sensitive and noble amperometric horseradish peroxidase (HRP) biosensor is fabricated via the deposition of gold nanoparticles (AuNPs) onto a three-dimensional (3D) porous carbonized chicken eggshell membrane (CESM). Due to the synergistic effects of the unique porous carbon architecture and well-distributed AuNPs, the enzyme-modified electrode shows an excellent electrochemical redox behavior. Compared with bare glass carbon electrode (GCE), the cathodic peak current of the enzymatic electrode increases 12.6 times at a formal potential of −100mV (vs. SCE) and charge-transfer resistance decreases 62.8%. Additionally, the AuNPs-CESM electrode exhibits a good biocompatibility, which effectively retains its bioactivity with a surface coverage of HRP 6.39×10−9 mol cm−2 (752 times higher than the theoretical monolayer coverage of HRP). Furthermore, the HRP-AuNPs-CESM-GCE electrode, as a biosensor for H2O2 detection, has a good accuracy and high sensitivity with the linear range of 0.01–2.7 mM H2O2 and the detection limit of 3μM H2O2 (S/N = 3).

A novel mechanism of bisphenol A removal during electro-enzymatic oxidative process: chain reactions from self-polymerization to cross-coupling oxidation.

The catalyzed removal of bisphenol A (BPA) by a horseradish peroxidase (HRP) cathode in the presence of humic acid (HA) was investigated. At an optimal condition, the removal of BPA achieved 100% within 2min reaction. In the electro-enzymatic process, products were analyzed by high performance liquid chromatography with diode array detector (HPLC-DAD) and high performance size exclusion chromatography (HPSEC). HPLC-DAD results showed that BPA was oxidized into self-polymers and then self-polymers as important intermediate products decreased and disappeared. HPSEC results showed the order of molecular weight (MW): HA+BPA cross-coupling products>HA self-coupling products>initial HA. According to above results, a novel mechanism of BPA transformation in the presence of HA was proposed in electro-enzymatic process. In summary, under oxidation of in situ hydrogen peroxide on HRP electrode, the BPA first are polymerized into self-polymers, and then, the polymers may be incorporated into HA matrix and finally larger MW of BPAn-HA might be formed. The presence of HA can provide chain reactions from BPA self-polymerization to cross-coupling oxidation. Therefore, in the presence of HA, the electro-enzymatic oxidation is an effective way to improve BPA removal.

Carbon materials derived from chitosan/cellulose cryogel-supported zeolite imidazole frameworks for potential supercapacitor application

In order to promote sustainable development, green and renewable clean energy technologies continue to be developed to meet the growing demand for energy, such as supercapacitor, fuel cells and lithium-ion battery. It is urgent to develop appropriate nanomaterials for these energy technologies to reduce the volume of the device, improve the efficiency of energy conversion and enlarge the energy storage capacity. Here, chitosan/cellulose carbon cryogel (CCS/CCL) were designed and synthesized. Through the introduction of zeolite imidazole frameworks (ZIFs) into the chitosan/cellulose cryogels, the obtained materials showed a microstructure of ZIF-7 (a kind of ZIFs) coated chitosan/cellulose fibers (CS/CL). After carbonizing, the as-prepared carbonized ZIF-7@cellulose cryogel (NC@CCL, NC is carbonized ZIF-7) and carbonized ZIF-7@chitosan cryogel (NC@CCS) exhibited suitable microspore contents of 34.37% and 30%, respectively, and they both showed an internal resistance lower than 2Ω. Thereby, NC@CCL and NC@CCS exhibited a high specific capacitance of 150.4Fg-1 and 173.1Fg-1, respectively, which were much higher than those of the original materials. This approach offers a facile method for improving the strength and electronic conductivity of carbon cryogel derived from nature polymers, and also efficiently inhibits the agglomeration of cryogel during carbonization in high temperature, which opens a novel avenue for the development of carbon cryogel materials for application in energy conversion systems.

Transformation, products, and pathways of chlorophenols via electro-enzymatic catalysis: How to control toxic intermediate products

Chlorophenols can be easily oxidized into chlorobenzoquinones (CBQs), which are highly toxic and have been linked to bladder cancer risk. Herein, we report the transformation, products, and pathways of 2,4-dichlorophenol (DCP) by horseradish peroxidase (HRP) and electro-generated hydrogen peroxide (H2O2) and suggest methods to control the formation of toxic intermediate products. After a 10-min electroenzymatic process, 99.7% DCP removal may be achieved under optimal conditions. A total of 16 reaction products, most of which are subsequently verified as DCP polymers and related quinone derivatives, are identified by using ultra-performance liquid chromatography-time-of-flight mass spectrometry (UPLC-TOF-MS). A five-step reaction pathway for DCP transformation, including HRP-driven substrate oxidation, substitution and radical coupling, quick redox equilibrium, nucleophilic reaction and precipitation from aqueous solution, is proposed. Current variations and the presence of CO2 could significantly affect these reaction pathways. In particular, higher currents enhance the hydroxylation process by promoting alkaline conditions and abundant H2O2 formation. As both OH(-) and H2O2 are strong nucleophiles, they easily react with CBQ products to form hydroxylated products, which can significantly reduce solution toxicity. An adequate supply of CO2 can provide favorable pH conditions and facilitate enzymatic steps, such as substrate oxidation and radical coupling, to generate precipitable polymerized products. All of the results suggest that toxic intermediate products can be effectively reduced and controlled during the electro-enzymatic process to remove DCP and other phenolic pollutants from wastewaters.

Surface Charge Research of Graphene Oxide, Chemically Reduced Graphene Oxide and Thermally Exfoliated Graphene Oxide

In this contribution, the surface electrical properties of graphene oxide (GO), chemically reduced graphene oxide (RGO) and thermally exfoliated graphene oxide (EGO) were characterized by zeta potential. Their surface morphologies were observed by scanning electron microscope. Then they were immobilized on glass carbon electrodes and their electrochemical behaviors for different charged redox systems were also investigated by using the cyclic voltammetry (CV) method. Results indicated that the density of surface negative charge on GO is much more than those on RGO and EGO. Furthermore, the electrochemical performances of electrodes modified with GO, RGO and EGO for detecting the model analyte Cu2+ by CV were compared. The results demonstrate that negative charge on the surface of graphene materials affects their performances as electrochemical sensors significantly.

Comprehensive evaluation on effective leaching of critical metals from spent lithium-ion batteries

Recovery of metals from spent lithium-ion batteries (LIBs) has attracted worldwide attention because of issues from both environmental impacts and resource supply. Leaching, for instance using an acidic solution, is a critical step for effective recovery of metals from spent LIBs. To achieve both high leaching efficiency and selectivity of the targeted metals, improved understanding on the interactive features of the materials and leaching solutions is highly required. However, such understanding is still limited at least caused by the variation on physiochemical properties of different leaching solutions. In this research, a comprehensive investigation and evaluation on the leaching process using acidic solutions to recycle spent LIBs is carried out. Through analyzing two important parameters, i.e. leaching speed and recovery rate of the corresponding metals, the effects of hydrogen ion concentration, acid species and concentration on these two parameters were evaluated. It was found that a leachant with organic acids may leach Co and Li from the cathode scrap and leave Al foil as metallic form with high leaching selectivity, while that with inorganic acids typically leach all metals into the solution. Inconsistency between the leaching selectivity and efficiency during spent LIBs recycling is frequently noticed. In order to achieve an optimal status with both high leaching selectivity and efficiency (especially at high solid-to-liquid ratios), it is important to manipulate the average leaching speed and recovery rate of metals to optimize the leaching conditions. Subsequently, it is found that the leaching speed is significantly dependent on the hydrogen ion concentration and the capability of releasing hydrogen ions of the acidic leachant during leaching. With this research, it is expected to improve understanding on controlling the physiochemical properties of a leaching solution and to potentially design processes for spent LIBs recycling with high industrial viability.

Emerging investigator series: Dispersed Transition Metal on Nitrogen Doped Carbon Nanoframework for Environmental Hydrogen Peroxide Detection

Hydrogen peroxide (H2O2) is a key species in many environmental processes such as the electro-Fenton system to remove organic pollutants in wastewater treatment. Traditional methods for measuring H2O2 are often complex and time-consuming. Due to their low cost and high catalytic activity, transition metals (TM) can be used as high-performance electrochemical sensing materials for detecting H2O2. However, the aggregation of metal atoms will severely limit their catalytic efficiency and exposure area. In this study, we explored a method to disperse TM homogeneously on a zeolitic imidazolate framework-8 (ZIF-8) derived nitrogen-doped carbon (N/C) nanoframework and used it as the electrocatalyst for detecting H2O2 in an electro-Fenton system. Cu and Mn were used as the examples. Benefitting from the homogeneously dispersed TM, the synthesized nanoframework with a low content of TM exhibits superior electrocatalytic activity and an anti-interference ability in detecting H2O2. It has a wide linear range (0.0005–50 mM for 1% Cu–N/C and 0.0001–50 mM for 1% Mn–N/C) and a low detection limit (0.047 μM for 1% Cu–N/C and 0.036 μM for 1% Mn–N/C). Using the synthesized nanoframework, a system for continuously detecting the H2O2 concentration in an electro-Fenton system in situ was presented. The reported method to fabricate such nanomaterials with a higher catalytic efficiency of TM has implications in other applications such as environmental treatment, catalysis, and energy conversion.

Chloro-benquinone Modified on Graphene Oxide as Metal-free Catalyst: Strong Promotion of Hydroxyl Radical and Generation of Ultra-Small Graphene Oxide

Carbon-based metal-free catalyst has attracted more and more attention. It is a big challenge to improve catalytic activity of metal-free catalyst for decomposition of H2O2 to produce hydroxyl radical (HO•). Here, we report chloro-benquinone (TCBQ) modified on graphene oxide (GO) as metal-free catalyst for strong promotion of HO•. By the incorporation of GO, the HO• production by H2O2 and TCBQ is significantly promoted. Based on density functional theory, TCBQ modified GO (GO-TCBQ) is more prone to be nucleophilic attacked by H2O2 to yield HO• via electron transfer acceleration. Furthermore, the generated HO• can cut GO nanosheets into uniform ultra-small graphene oxide (USGO) through the cleavage of epoxy and C-C bonds. Interestingly, the damaged GO and in situ formed GO fragments can further enhance decomposition of H2O2 to produce HO•. Different from other catalytic processes, the GO-TCBQ metal-free catalysis process can be enhanced by GO itself, producing more HO•, and uniform USGO also can be generated. Thus, the metal free catalysis will be considered a fabrication method for uniform USGO, and may be extended to other fields including detoxifying organic pollutants and the application as disinfectants.