Ternary Composite of Polyaniline Graphene and TiO2 as a Bifunctional Catalyst to Enhance the Performance of Both the Bioanode and Cathode of a Microbial Fuel Cell

Carbon paper anodes decorated with TiO2 nanowires and Au nanoparticles for facilitating bacterial extracellular electron transfer

Au nanoparticles-composite TiO2 nanowires (NWs) modified carbon paper (CP) anode was synthesized via the hydrothermal method. Field emission scanning electron microscopy (FESEM) images demonstrate that the modified nanocomposite electrode features a rough and bumpy surface structure. The electrochemical activities of TiO2-Au/CP and the control electrodes (TiO2-NWs/CP, Au/CP, CP) for microbial fuel cell (MFC) are investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). When using TiO2-Au/CP as a bioanode, the maximum power output density of Shewanella loihica PV-4 inoculated MFC increases by 49.7%, 26.5% and 190.6% compared with that when using TiO2-NWs/CP, Au/CP and bare CP as bioanodes, respectively. CV analysis indicates that TiO2-Au mediates direct and indirect electron transfer between the electrode and the bacteria, as evidenced by the appearance of redox peaks with mid-point potentials Em of - 0.305 V and -0.465 V, respectively. The generation of bioelectricity reveals the formation of a biofilm on the electrode surface. Furthermore, compared with the control electrodes, the MFC assembled with a TiO2-Au anode exhibits a smaller semicircle in the high-frequency region, representing a lower charge transfer resistance (Rct). The improvement in MFC performance can be attributed to the fact that the combination of TiO2 and Au enhances the conductivity and electrochemical activity of the electrode, along with its good biocompatibility and large specific surface area, which are favorable for bacterial colonization. Thus, TiO2-Au/CP serves as an ideal anode material featuring simple synthesis. Additionally, its surface modifier, TiO2-Au can be extended for the modification of other base electrodes, enabling the acquisition of high-quality anodes for MFCs.

Conductive Polymers and Their Nanocomposites: Application Features in Biosensors and Biofuel Cells

Conductive polymers and their composites are excellent materials for coupling biological materials and electrodes in bioelectrochemical systems. It is assumed that their relevance and introduction to the field of bioelectrochemical devices will only grow due to their tunable conductivity, easy modification, and biocompatibility. This review analyzes the main trends and trends in the development of the methodology for the application of conductive polymers and their use in biosensors and biofuel elements, as well as describes their future prospects. Approaches to the synthesis of such materials and the peculiarities of obtaining their nanocomposites are presented. Special emphasis is placed on the features of the interfaces of such materials with biological objects.

Synergistic effect of TiO2 nanostructured cathode in microbial fuel cell for bioelectricity enhancement

Nano-bedecking of electrode with nanoparticles is an effective method to improve power generation of microbial fuel cells (MFCs). In this study, different concentrations (0.25 mg cm^-2, 0.50 mg cm^-2, 0.75 mg cm^-2 and 1.0 mg cm^-2) of TiO₂ nanoparticles of size 10-25 nm were overlaid on the carbon cloth (CC) using spray pyrolysis technique and used as catalytic cathode in a dual-chambered microbial fuel cell treating distillery wastewater. Results evidenced that TiO₂ nanoparticles modified cathode increased the power generation and recorded a highest power and current density of 162.5 ± 2 mW m^-2 and 1.4 ± 0.005 A m^-2, respectively. Carbon cloth coated with 0.50 mg cm^-2 TiO₂ nanoparticles showed 2.8 and 7.3 times higher current and power density as compared to uncoated cathode. MFC operated at a hydraulic retention time (HRT) and organic loading rate (OLR) of 72 h and 59.2 g COD L^-1 d^-1 showed a maximum chemical oxygen demand (COD) removal of 72.3% which was 15.3% higher than the control MFC. Likewise, the coulombic efficiency of control and modified MFC was 33% and 44%, respectively. The maximum NO₃^-- N, NO₂^-- N and NH₄⁺- N removal efficiency of 77.3%, 49.9% and 59.4% were observed for TiO₂ nanoparticles modified electrode which was 19.3%, 11.4% and 10.5% higher than control. TiO₂ modified cathode was effective in enhancing the bioelectricity generation in MFCs.

Rice husk-derived silicon nanostructured anode to enhance power generation in microbial fuel cell treating distillery wastewater

The present study aims to utilize rice husk as a source of silica to prepare rice husk derived silicon nanoparticles (RH-Si) and demonstrate its ability as an anode modifier in a two-chambered H-shaped microbial fuel cell (MFC). The silicon nanoparticles synthesized by magnesiothermal reduction process were spherical in shape and ranged in size from 15 to 60 nm. The anode modified with silicon nanoparticles of 0.50 mg cm^-2 recorded the maximum power and current density of 190.5 mW m^-2 and 1.5 A m^-2 corresponding to 7.6-fold and 3-fold increase as compared to the control . The modified anode also recorded a COD removal and coulombic efficiency of 74% and 49%, respectively in MFC operated with combined distillery and domestic wastewater at a HRT and OLR of 72 h and 59.2 gCOD L^-1 d^-1, respectively. The results evidence that RH derived silicon NPs are good anode modifiers and effective in enhancing bioelectricity generation and COD removal in MFCs.

A review of graphene-TiO2 and graphene-ZnO nanocomposite photocatalysts for wastewater treatment

Technologies for wastewater remediation have been growing ever since the environmental and health concern is realized. Development of nanomaterials has enabled mankind to have different methods to treat the various kinds of inorganic and organic pollutants present in wastewater from many resources. Among the many materials, semiconductor materials have found many environmental applications due to their outstanding photocatalytic activities. TiO₂ and ZnO are more effectively used as photocatalyst or adsorbents in the withdrawal of inorganic as well as organic wastes from the wastewater. On the other hand, graphene is tremendously being investigated for applications in environmental remediation in view of the superior physical, optical, thermal, and electronic properties of graphene nanocomposites. In this work, graphene-TiO₂ and graphene-ZnO nanocomposites have been reviewed for photocatalytic wastewater treatment. The various preparation techniques of these nanocomposites have been discussed. Also, different design strategies for graphene-based photocatalyst have been revealed. These nanocomposites exhibit promising applications in most of the water purification processes which are reviewed in this work. Along with this, the development of these nanocomposites using biomass-derived graphene has also been introduced. PRACTITIONER POINTS: Graphene-TiO₂ and graphene-ZnO nanocomposites are effective for wastewater treatment through photocatalysis. These nanocomposite photocatalysts have been used in the form of membrane as well as antibacterial agents. Synthetic strategies and design considerations of graphene-based photocatalyst play a major role. Biomass-derived graphene-TiO₂ and graphene-ZnO nanocomposites have also found application in wastewater treatment.

Current Progress of Interfacing Organic Semiconducting Materials with Bacteria

Microbial bioelectronics require interfacing microorganisms with electrodes. The resulting abiotic/biotic platforms provide the basis of a range of technologies, including energy conversion and diagnostic assays. Organic semiconductors (OSCs) provide a unique strategy to modulate the interfaces between microbial systems and external electrodes, thereby improving the performance of these incipient technologies. In this review, we explore recent progress in the field on how OSCs, and related materials capable of charge transport, are being used within the context of microbial systems, and more specifically bacteria. We begin by examining the electrochemical communication modes in bacteria and the biological basis for charge transport. Different types of synthetic organic materials that have been designed and synthesized for interfacing and interrogating bacteria are discussed next, followed by the most commonly used characterization techniques for evaluating transport in microbial, synthetic, and hybrid systems. A range of applications is subsequently examined, including biological sensors and energy conversion systems. The review concludes by summarizing what has been accomplished so far and suggests future design approaches for OSC bioelectronics materials and technologies that hybridize characteristic properties of microbial and OSC systems.

TiO2-Graphene Quantum Dots Nanocomposites for Photocatalysis in Energy and Biomedical Applications

The focus of current research in material science has shifted from “less efficient” single-component nanomaterials to the superior-performance, next-generation, multifunctional nanocomposites. TiO2 is a widely used benchmark photocatalyst with unique physicochemical properties. However, the large bandgap and massive recombination of photogenerated charge carriers limit its overall photocatalytic efficiency. When TiO2 nanoparticles are modified with graphene quantum dots (GQDs), some significant improvements can be achieved in terms of (i) broadening the light absorption wavelengths, (ii) design of active reaction sites, and (iii) control of the electron-hole (e−-h+) recombination. Accordingly, TiO2-GQDs nanocomposites exhibit promising multifunctionalities in a wide range of fields including, but not limited to, energy, biomedical aids, electronics, and flexible wearable sensors. This review presents some important aspects of TiO2-GQDs nanocomposites as photocatalysts in energy and biomedical applications. These include: (1) structural formulations and synthesis methods of TiO2-GQDs nanocomposites; (2) discourse about the mechanism behind the overall higher photoactivities of these nanocomposites; (3) various characterization techniques which can be used to judge the photocatalytic performance of these nanocomposites, and (4) the application of these nanocomposites in biomedical and energy conversion devices. Although some objectives have been achieved, new challenges still exist and hinder the widespread application of these nanocomposites. These challenges are briefly discussed in the Future Scope section of this review.

Performance evaluation of poly(aniline-co-pyrrole) wrapped titanium dioxide nanocomposite as an air-cathode catalyst material for microbial fuel cell

A simple, inexpensive in situ oxidative polymerization of aniline and pyrrole using ammonium persulfate (APS) as oxidant and hydrochloric acid (HCl) as dopant has been used to synthesize a hybrid (PAni-Co-PPy)@TiO₂ nanocomposite with titanium oxide (TiO₂) nanoparticles (NPs) wrapped into (PAni-Co-PPy) copolymer. The synthesized nanocomposite has been shown with higher oxygen reduction reactions (ORR) as an excellent cathode material for higher performance in the complex of (PAni-Co-PPy)⁺/TiO₂(O^-). The charge transport phenomenon between TiO₂ and (PAni-Co-PPy)⁺ were found adequate with subsequent delocalization of electron/s at PAni and PPy. The self-doping nature of TiO₂ (O^-) played a vital role in oxygen adsorption and desorption process. With higher electrical conductivity and surface area, these were tested in microbial fuel cells (MFCs) for ORRs at cathode. This yielded a relatively higher current and power density output as compared to PAni@TiO₂, PPy@TiO₂, and commercially available Pt/C cathode catalysts in MFC system. In overall, the prepared (PAni-Co-PPy)@TiO₂ nano-hybrid cathode delivered ~2.03 fold higher power density as compared to Pt/C catalyst, i.e. ~987.36 ± 49 mW/m² against ~481.02 ± 24 mW/m². The properties of electro-catalysts established an improved synergetic effect between TiO₂ NPs and (PAni-Co-PPy). In effect, the enhanced surface area and electrochemical properties of the prepared (PAni-Co-PPy)@TiO₂ nano-hybrid system is depicted here as an effective cathode catalyst in MFCs for improved performance.

Nitrogen-rich graphitic-carbon@graphene as a metal-free electrocatalyst for oxygen reduction reaction

The metal-free nitrogen-doped graphitic-carbon@graphene (Ng-C@G) is prepared from a composite of polyaniline and graphene by a facile polymerization following by pyrolysis for electrochemical oxygen reduction reaction (ORR). Pyrolysis creates a sponge-like with ant-cave-architecture in the polyaniline derived nitrogenous graphitic-carbon on graphene. The nitrogenous carbon is highly graphitized and most of the nitrogen atoms are in graphitic and pyridinic forms with less oxygenated is found when pyrolyzed at 800 °C. The electrocatalytic activity of Ng-C@G-800 is even better than the benchmarked Pt/C catalyst resulting in the higher half-wave potential (8 mV) and limiting current density (0.74 mA cm^-2) for ORR in alkaline medium. Higher catalytic performance is originated from the special porous structure at microscale level and the abundant graphitic- and pyridinic-N active sites at the nanoscale level on carbon-graphene matrix which are beneficial to the high O₂-mass transportation to those accessible sites. Also, it possesses a higher cycle stability resulting in the negligible potential shift and slight oxidation of pyridinic-N with better tolerance to the methanol.

Vertical alignment of polyaniline nanofibers on electrode surface for high-performance microbial fuel cells

Electrode modifications with conductive and nanostructured polyaniline (PANI) were recognized as efficient approach to improve interaction between electrode surface and electrogenic bacteria for boosting the performance of microbial fuel cell (MFC). However, it still showed undesirable performance because of the challenge to control the orientation (such as vertical alignment) of PANI nanostructure for extracellular electron transfer (EET). In this work, vertically aligned polyaniline (VA-PANI) on carbon cloth electrode surface were prepared by in-situ polymerization method (simply tuning the ratio of tartaric acid (TA) dopant). Impressively, the VA-PANI greatly improved the EET due to the increased opportunity to connect with conductive proteins. Eventually, MFC equipped with the VA-PANI electrodes delivered a power output of 853 mW/m², which greatly outperformed those electrodes modified with un-oriented PANI. This work provided the possibility to control the orientation of PANI for EET and promise to harvest energy from wastewater with MFC.