Sandesh Y. Sawant

Three-dimensional, highly porous N-doped carbon foam as microorganism propitious, efficient anode for high performance microbial fuel cell

Three-dimensional (3D) N-doped open-porous carbon foam was fabricated using the simple procedure of calcining a melamine sponge. The properties of the fabricated carbon foam and its performance in microbial fuel cells (MFCs) using Shewanella oneidensis MR-1 (S. oneidensis) were compared with those of commercial graphite felt. The MFC with the carbon foam anode produced approximately 2 times higher power density than the commercial graphite felt. The superior performance of the as-prepared carbon foam in MFC was attributed to the higher surface area (687.19 m2 g−1) and open-porous scaffold structure. Moreover, the appearance of the hydrophilic functional groups such as CN–C, N–CO on the surface of the as-prepared carbon foam facilitated extracellular electron transfer, resulting in a decrease in charge transfer resistance and an increase in biocompatibility. Owing to the excellent biocompatibility, a large amount of microbial biomass colonized both the surface and inside the carbon foam, which helped enhance the performance of the MFC.

Anchoring Mechanism of ZnO Nanoparticles on Graphitic Carbon Nanofiber Surfaces through a Modified Co-Precipitation Method to Improve Interfacial Contact and Photocatalytic Performance

A facile three-step co-precipitation method is developed to synthesize graphitic carbon nanofibers (CNFs) decorated with ZnO nanoparticles (NPs). By interchanging intermediate steps of the reaction processes, two kinds of nanohybrids are fabricated with stark morphological and physicochemical differences. The morphologies differ because of the different chemical environments of the NP/nanocluster formation. The hybrid with larger and non-uniform ZnO nanocluster size is formed in liquid phase and resulted in considerable interfacial defects that deteriorate the charge-transfer properties. The hybrid with smaller and uniform ZnO NPs was formed in a dry solid phase and produced near-defect-free interfaces, leading to efficient charge transfer for superior photocatalytic performance. The results broaden the understanding of the anchoring/bonding mechanism in ZnO/CNF hybrid formation and may facilitate further development of more effective exfoliation strategies for the preparation of high-performance composites/hybrids.

Metal-Free Carbon-Based Materials: Promising Electrocatalysts for Oxygen Reduction Reaction in Microbial Fuel Cells

Microbial fuel cells (MFCs) are a promising green approach for wastewater treatment with the simultaneous advantage of energy production. Among the various limiting factors, the cathodic limitation, with respect to performance and cost, is one of the main obstacles to the practical applications of MFCs. Despite the high performance of platinum and other metal-based cathodes, their practical use is limited by their high cost, low stability, and environmental toxicity. Oxygen is the most favorable electron acceptor in the case of MFCs, which reduces to water through a complicated oxygen reduction reaction (ORR). Carbon-based ORR catalysts possessing high surface area and good electrical conductivity improve the ORR kinetics by lowering the cathodic overpotential. Recently, a range of carbon-based materials have attracted attention for their exceptional ORR catalytic activity and high stability. Doping the carbon texture with a heteroatom improved their ORR activity remarkably through the favorable adsorption of oxygen and weaker molecular bonding. This review provides better insight into ORR catalysis for MFCs and the properties, performance, and applicability of various metal-free carbon-based electrocatalysts in MFCs to find the most appropriate cathodic catalyst for the practical applications. The approaches for improvement, key challenges, and future opportunities in this field are also explored.

Facile electrochemical assisted synthesis of ZnO/graphene nanosheets with enhanced photocatalytic activity

In the present study, an electrochemical exfoliation technique was used to synthesize a series of zinc oxide/graphene (ZnO/Gr) nanocomposites using different concentrations of zinc nitrate in an electrolyte solution. The prepared ZnO/Gr nanocomposites were characterized using a range of analytical techniques and evaluated further for their photocatalytic activity over methyl orange (MO) and rhodamine B (RhB) under UV light. Scanning electron microscopy and transmission electron microscopy showed that the ZnO/Gr nanocomposite synthesized using 7 mmol of zinc nitrate exhibited a sheet-like morphology with a uniform decoration of ZnO nanoparticles over the graphene sheets, as well as the maximum photodegradation capacity for MO (>96%) and RhB (>89%) among the composites prepared. The loading of graphene was found to be crucial for deciding the enhancement in the photocatalytic activity, and resulted in a remarkable improvement in photocatalytic activity (∼7 times for MO and ∼2 times for RhB) over bare ZnO. Photoluminescence spectroscopic analysis revealed the improved separation of electron–hole pairs with the graphene loading, which is mainly responsible for the enhanced photocatalytic activity. The present work possesses the advantage of in situ synthesis of few layered less defective graphene/ZnO composites with enhanced photocatalytic activity.

Facile and single-step route towards ZnO@C core–shell nanoparticles as an oxygen vacancy induced visible light active photocatalyst using the thermal decomposition of Zn(an)2(NO3)2

Zinc oxide–carbon (ZnO@C) core–shell nanoparticles were synthesized using a facile and single-step method, which involved the thermal degradation of a zinc aniline nitrate complex in methanol. The formation of ZnO and carbon was observed during the early stages of synthesis (>200 °C), whereas a further increase in the temperature determines the level of the carbon coating. Transmission electron microscopy confirmed that the ZnO@C nanoparticles obtained at 600 °C were ∼100 nm in size with a uniform 5–20 nm thick carbon coating. The nano-coating of carbon on ZnO along with the presence of oxygen vacancies promoted its photocatalytic activity under visible light with higher efficiency for the photodegradation of rhodamine B than bare ZnO. The two probable pathways for the visible activity and the enhanced photodegradation capacity of ZnO@C core–shell nanoparticles are also discussed. The synthesized ZnO@C core–shell nanoparticles exhibited very good stability and recyclability, highlighting their potential use as an efficient visible light driven photocatalyst for pollutant degradation.

Electrochemically active biofilm-assisted biogenic synthesis of an Ag-decorated ZnO@C core–shell ternary plasmonic photocatalyst with enhanced visible-photocatalytic activity

Colonies of electrochemically active microorganisms called electroactive biofilms (EABs) have potential applications in bioenergy and chemical production. In the present study, an EAB was used as a reducing tool to synthesize Ag-decorated ZnO@C core–shell (Ag–ZnO@C) ternary plasmonic photocatalysts. A simple thermal decomposition route was followed to synthesize ZnO@C nanoparticles using a zinc aniline nitrate complex. The simultaneous adsorption of Ag+ in the carbon shell of the ZnO@C particles during reduction using an EAB allowed the direct contact among Ag nanoparticles, the ZnO core, and the carbon shell. Therefore, the synthesized Ag–ZnO@C ternary photocatalysts showed a stronger interconnection among all the components, which allowed the easy transfer of photogenerated charges and provided enhanced charge carrier separation. Optical characterization showed that the enhanced absorption of visible light along with a decrease in the band gap and a red shift in the valence band maximum occurred due to the decoration of Ag-nanoparticles on ZnO@C. Ag–ZnO@C exhibited higher photocatalytic activity for the degradation of rhodamine blue and 4-nitrophenol under visible light irradiation than ZnO@C and bare ZnO without any significant loss after five successive cycles. Finally, a possible photocatalytic mechanism for charge transfer was proposed to explain the enhanced photocatalytic performance of the Ag–ZnO@C ternary photocatalyst. This study provides insights into the ternary photocatalytic system with a core–shell material and offers a biogenic route for the facile fabrication of Ag–ZnO@C photocatalysts.

Porous synthetic hectorite clay-alginate composite beads for effective adsorption of methylene blue dye from aqueous solution

The present study deals with the preparation and characterization of mesoporous synthetic hectorite (MSH) clay which further encapsulated with Na-alginate for the preparation of mesoporous synthetic hectorite-alginate beads (MSH-AB) where Ca2+ act as a cross-linking agent. The detail characterization of MSH and MSH-AB were carried out by various physicochemical techniques. The thermogravimetric analysis study showed better thermal stability results for MSH-AB. The textural properties results of MSH and MSH-AB showed the high surface area 468, 205m2/g, and the pore volume of 0.34, 0.29cm3/g respectively. The applicability of powder MSH and MSH-AB in wet (W) and dry (D) forms were assessed for the removal of cationic dye, methylene blue (MB) by optimizing various batch adsorption parameters. The Langmuir monolayer adsorption capacity obtained for MSH-AB-W showed significant high adsorption efficacy (i.e., 785.45mgMB/g) compared to the MSH-AB-D (357.14mgMB/g) and powder MSH materials (196.00mgMB/g). The adsorption isotherm studies showed that the Langmuir isotherm model was best suitable for MSH, whereas the Freundlich model was utilised to describe the adsorption behavior of organized hydrogel composite beads. The pseudo-second-order kinetics model was observed best for MB sorption onto MSH, whereas pseudo-first order useful to describe the kinetic behavior of MSH-AB. The regeneration experimental results revealed that MSH-AB-W could be recycled more than six cycles with high MB removal efficiency. Furthermore, the adsorption property of the MSH-AB-W was examined for the binary mixture of MB with other dye solutions such as Methyl Red (MR), Methyl Orange (MO), Alizarine Yellow (AY), and Remazol Brilliant Blue (RBB) to evaluate the selective adsorption efficiency. The MSH composite beads were found potentially suitable as an efficient, selective and recyclable adsorbent for the removal of MB from the aqueous solutions.

Development of Suitable Anode Materials for Microbial Fuel Cells

Microbial fuel cells (MFCs) and related bioelectrochemical systems (BESs) have shown impressive developments for many purposes over the past decade (Kalathil et al. 2012; Han et al. 2013, 2014, 2016). Even with the noticeable improvements in power density, the large-scale application of MFCs is still limited due to the low power generation and high cost (Wei et al. 2011). To take this technology from laboratory-scale research to commercial applications, the cost and the performance of these systems need to be optimized further. The anode electrode plays an important role in the performance and cost of MFCs. The electrode materials in MFCs have some general and individual characteristics. In general, electrode materials must have good conduction, excellent biocompatibility, good chemical stability, high mechanical strength and low cost. The anode material design has attracted an enormous number of studies over the past decade.