Kunal Mondal

Reusable electrospun mesoporous ZnO nanofiber mats for photocatalytic degradation of polycyclic aromatic hydrocarbon dyes in wastewater

We demonstrate a new method for the fabrication of free-standing mats of mesoporous ZnO nanofibers by electrospinning a blend of zinc acetate with a carrier polymer, polyacrylonitrile (PAN) in N,N-dimethyl-formamide (DMF) solvent. Decomposition of PAN by calcination produces porous ZnO nanofibers with fiber diameters in the range of 50-150 nm depending on the electrospinning conditions such as the precursor solution concentration, electric field strength, and solution flow rate. The fibers are characterized for their morphology, phase composition, band gap, crystallinity, surface area, and porosity. In this paper, optimized mats of ZnO nanofibers with an average fiber diameter of 60 nm are shown to be highly effective in the photocatalytic degradation of the PAH dyes--naphthalene and anthracene. Nanofiber mats fabricated here may also find applications in gas sensing, piezoelectric devices, optoelectronics, and photocatalysis.

Highly Sensitive Biofunctionalized Mesoporous Electrospun TiO2 Nanofiber Based Interface for Biosensing

The surface modified and aligned mesoporous anatase titania nanofiber mats (TiO2-NF) have been fabricated by electrospinning for esterified cholesterol detection by electrochemical technique. The electrospinning and porosity of mesoporous TiO2-NF were controlled by use of polyvinylpyrrolidone (PVP) as a sacrificial carrier polymer in the titanium isopropoxide precursor. The mesoporous TiO2-NF of diameters ranging from 30 to 60 nm were obtained by calcination at 470 °C and partially aligned on a rotating drum collector. The functional groups such as -COOH, -CHO etc. were introduced on TiO2-NF surface via oxygen plasma treatment making the surface hydrophilic. Cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) were covalently immobilized on the plasma treated surface of NF (cTiO2-NF) via N-ethyl-N0-(3-dimethylaminopropyl carbodiimide) and N-hydroxysuccinimide (EDC-NHS) chemistry. The high mesoporosity (∼61%) of the fibrous film allowed enhanced loading of the enzyme molecules in the TiO2-NF mat. The ChEt-ChOx/cTiO2-NF-based bioelectrode was used to detect esterified cholesterol using electrochemical technique. The high aspect ratio, surface area of aligned TiO2-NF showed excellent voltammetric and catalytic response resulting in improved detection limit (0.49 mM). The results of response studies of this biosensor show excellent sensitivity (181.6 μA/mg dL(-1)/cm(2)) and rapid detection (20 s). This proposed strategy of biomolecule detection is thus a promising platform for the development of miniaturized device for biosensing applications.

Microfluidic Immuno-Biochip for Detection of Breast Cancer Biomarkers Using Hierarchical Composite of Porous Graphene and Titanium Dioxide Nanofibers

We report on a label-free microfluidic immunosensor with femtomolar sensitivity and high selectivity for early detection of epidermal growth factor receptor 2 (EGFR2 or ErbB2) proteins. This sensor utilizes a uniquely structured immunoelectrode made of porous hierarchical graphene foam (GF) modified with electrospun carbon-doped titanium dioxide nanofibers (nTiO2) as an electrochemical working electrode. Due to excellent biocompatibility, intrinsic surface defects, high reaction kinetics, and good stability for proteins, anatase nTiO2 are ideal for electrochemical sensor applications. The three-dimensional and porous features of GF allow nTiO2 to penetrate and attach to the surface of the GF by physical adsorption. Combining GF with functional nTiO2 yields high charge transfer resistance, large surface area, and porous access to the sensing surface by the analyte, resulting in new possibilities for the development of electrochemical immunosensors. Here, the enabling of EDC-NHS chemistry covalently immobilized the antibody of ErbB2 (anti-ErbB2) on the GF-nTiO2 composite. To obtain a compact sensor architecture, the composite working electrode was designed to hang above the gold counter electrode in a microfluidic channel. The sensor underwent differential pulse voltammetry and electrochemical impedance spectroscopy to quantify breast cancer biomarkers. The two methods had high sensitivities of 0.585 μA μM(-1) cm(-2) and 43.7 kΩ μM(-1) cm(-2) in a wide concentration range of target ErbB2 antigen from 1 × 10(-15) M (1.0 fM) to 0.1 × 10(-6) M (0.1 μM) and from 1 × 10(-13) M (0.1 pM) to 0.1 × 10(-6) M (0.1 μM), respectively. Utilization of the specific recognition element, i.e., anti-ErbB2, results in high specificity, even in the presence of identical members of the EGFR family of receptor tyrosine kinases, such as ErbB3 and ErbB4. Many promising applications in the field of electrochemical detection of chemical and biological species will derive from the integration of the porous GF-nTiO2 composite into microfluidic devices.

Recent advances in the synthesis and application of photocatalytic metal–metal oxide core–shell nanoparticles for environmental remediation and their recycling process

Core–shell nanoparticles are a special category of materials with nanostructures that have obtained more attention in recent times owing to their fascinating properties and extensive choice of applications in catalysis, photocatalysis, materials chemistry, biology, drug delivery, sensors and other electronic device applications. By wisely modifying the cores along with the shells material and morphology, a variety of core–shell nanostructures can be created with tunable properties that can perform vital roles in several catalytic and photocatalytic developments and promise sustainable solutions to current environmental remediation problems. Recently, the development of core–shell nanoparticles with Au, Ag, Pt, Pd, Zn, Ni etc. metals as a core and ZnO, TiO2, SiO2, Cu2O, Fe2O3 and SnO2 etc. metal oxide semiconductors as a shell has engrossed huge research interest in catalysis, photocatalysis, solar photovoltaics and so on owing to their tunable nanoscale functionalities in the core and shell particles. This review covers the core–shell nanomaterials, mainly, metal–metal oxide core–shell nanostructures with an overview of the recent advances in their synthesis, and applications. It includes a critical review of application of these materials towards photocatalytic wastewater purification and bacterial disinfections under UV and visible light irritation. It also includes a brief discussion on mechanisms of heterogeneous and homogeneous photocatalysis and the effect of different morphologies of photocatalysts in view of photocatalysis for wastewater treatment. Finally, recycling, reuse and actual photocatalysis in a photocatalytic reactor of core–shell nanostructures have also been discussed which is very important for a sustainable wastewater treatment. The future prospects of such core–shell nanoparticles for cancer treatment by hyperthermia, drug delivery and several other interesting applications have been covered with a distinct emphasis on their structural depending properties.

Mesoporous Few-Layer Graphene Platform for Affinity Biosensing Application.

A label-free, highly reproducible, sensitive, and selective biosensor is proposed using antiapolipoprotein B 100 (AAB) functionalized mesoporous few-layer reduced graphene oxide and nickel oxide (rGO-NiO) nanocomposite for detection of low density lipoprotein (LDL) molecules. The formation of mesoporous rGO-NiO composite on indium tin oxide conductive electrode has been accomplished via electrophoretic technique using colloidal suspension of rGO sheets and NiO nanoparticles. This biosensor shows good stability obtained by surface conjugation of antibody AAB molecules with rGO-NiO matrix by EDC-NHS coupling chemistry. The defect-less few layer rGO sheets, NiO nanoparticles (nNiO) and formation of nanocomposite has been confirmed by Raman mapping, electron microscopic studies, X-ray diffraction, and electrochemical techniques. The synthesized rGO-NiO composite is mesoporous dominated with a small percentage of micro and macroporous structure as is evident by the results of Brunauer-Emmett-Teller experiment. Further, the bioconjugation of AAB with rGO-NiO has been investigated by Fourier transform-infrared spectroscopy studies. The kinetic studies for binding of antigen-antibody (LDL-AAB) and analytical performance of this biosensor have been evaluated by the impedance spectroscopic method. This biosensor exhibits an excellent sensitivity of 510 Ω (mg/dL)(-1) cm(-2) for detection of LDL molecules and is sensitive to 5 mg/dL concentration of LDL in a wide range of 0-130 mg/dL. Thus, this fabricated biosensor is an efficient and highly sensitive platform for the analysis of other antigen-antibody interactions and biomolecules detection.

Quantum dot sensitized electrospun mesoporous titanium dioxide hollow nanofibers for photocatalytic applications

In this work, mesoporous, hollow TiO2 nanofibers were fabricated by a coaxial electrospinning technique for the photocatalytic degradation of para-nitrophenol (4-NP), a well-known model water pollutant dye. The as-synthesized hollow nanofibers were sensitized by cadmium sulphide (CdS) quantum dots (QDs) through successive ion layer adsorption and reaction (SILAR) method for different deposition cycles. The CdS QDs loaded hollow TiO2 nanofibers (TiO2/CdS) harvest catalytic spots at the QDs and TiO2 interface which helps in enhanced exciton separation. The hollow and porous TiO2/CdS photocatalyst enhances absorption of UV and visible light due to presence of CdS QDs on the nanofiber surfaces. The resultant CdS QDs synthesized hollow TiO2 nanofibers exhibit excellent photocatalytic activity as shown with the degradation of 4-NP dye in aqueous medium. The photocatalytic degradation study was probed spectrophotometrically by measuring the absorbance of the degraded 4-NP solution using a UV-Vis absorption spectrophotometer. The effect of CdS QDs deposition cycles on dye degradation performance was also studied for TiO2/CdS nanofibers. TiO2/CdS photocatalyst for 3 SILAR deposition cycles was found to be ∼3 times more efficient than hollow TiO2 nanofibers and ∼8 times effective than the solid nanofibers. These nanofibers are reusable and their nanostructures do not change after repetitive usage. Such pristine and QDs sensitized hollow TiO2 nanofibers are thus a promising platform for the development of photocatalytic wastewater treatment and other applications such as photocatalytic water splitting, sensors, Li-ion batteries, and supercapacitor electrodes.

Recent advances in electrospun metal-oxide nanofiber based interfaces for electrochemical biosensing

The use of unique nanostructured materials has gained substantial importance in the field of biosensing and biomedical applications. Recently, the electrospinning technique has attracted immense attention in the development of nanofiber-based biosensors. Electrospinning has been accepted as a proficient practice for the fabrication of polymer, metal and metal-oxide nanofibers. Electrospinning appears to be the ultimate technique to generate biocompatible and biodegradable polymer/metal-oxide nanofibers, such as carbon, ZnO, TiO2, and NiO, for highly sensitive biosensing applications. Biosensors with enhanced sensitivity are becoming fascinating for the sensing of blood, and in particular for glucose, cholesterol, triglyceride, and low density lipoprotein (LDL) affinity sensing. Electrospinning can deposit a three-dimensional porous nanofibrous mat network on the surface of a sensor transducer, which provides a large global pore volume, predictable pore size distribution, and tunable interconnected porosity. These features of nanofibers can add further suitable functionalities to a sensor for the detection of bio-analytes in a specific environment, where efficient mass transport is needed towards the electrode surface. Electrospun fibers are able to form a highly porous nanofibrous web and their huge surface to volume ratios could lead to very high sensitivity due to their exceptional specific surface areas and interesting nanostructured morphologies, which give rise to properties that do not exist in fibers or wires with a bigger size. Based on the distinctive properties of electrospun nanofibers in the nanoscale that differentiate them from other nanostructures created by other existing methods, we describe in this review the knowledge on nanofibers suitable for biosensor and biomedical applications, including structure and property characterization. Additionally, information on polymers together with metal-oxides precursors and their processing conditions for the electrospinning of ultrafine metal-oxide fibers is briefly described in this paper. Additional relevant issues concerning the research challenges, technology limitations, and future trends are also discussed.

Superhydrophobic polymethylsilsesquioxane pinned one dimensional ZnO nanostructures for water remediation through photo-catalysis

ZnO nanostructures have been heavily explored for a variety of sensing properties and of late a major emphasis by researchers has been to find applications for ZnO materials in the domain of photo-catalysis. ZnO nanoparticles have been found as a better alternative to other materials for removing organic dyes from polluted water and the abolition of several hazardous materials etc. In this work we have developed ultra-dense high aspect ratio ZnO nano-forest like structures and explored their potential as photo-catalysts. The films formulated are superhydrophobic (contact angle ∼ 154°) in nature and have been evaluated as containing a high density of oxygen defects in the crystalline state of the ZnO (as validated through photoluminescence measurements). The samples were found to possess enhanced photo-catalytic properties, as measured through a dye degradation process using an UV-Vis spectrophotometer. These photo-catalytic properties may be due to the high defect density and also the enhanced area of the interactive surface as one goes from nano-particles to nano-rod like structures. The paper gives an insight into highly unique carpeted nano-wire bundles of ZnO and offers immense utility to the realization of high efficiency remediation filters.

One-step sol–gel synthesis of hierarchically porous, flow-through carbon/silica monoliths

Hierarchically porous, flow-through carbon/silica bicontinuous composite monoliths with ultra-high Brunauer–Emmett–Teller (BET) surface areas and tunable porosity in micro/meso/macro-structured domains, were obtained from an efficient one-step sol–gel chemistry based on the co-assembly of organic and inorganic precursors with simultaneous polymerization-induced phase separation. Without activation, the bicontinuous composites were subjected to pyrolysis and silica removal to yield crack-free hierarchically porous carbon monoliths that have large pore volumes and high BET surface areas (∼2600 m2 g−1). The removal of carbon from the silica/carbon composite monolith produces a microporous silica framework (BET area ∼600 m2 g−1). The hierarchically porous carbon monoliths were characterized in terms of their pore morphology, flow-through porosity, phase composition, mechanical strength, structural and elemental compositions, and surface wettability. The polymer monolith was determined to be hydrophobic, whereas the carbon monolith was hydrophilic in nature. The water permeability of the carbon monolith was determined to be 12 × 10−12 m2, and its Youngs modulus was 0.42 MPa, which suggests that this monolith could be used as a potential flow-through medium. The use of the carbon monolith as a catalytic support is demonstrated by the in situ growth of silver nanoparticles, with which the hybrid exhibits excellent catalytic activity for the reduction of 4-nitrophenol (4-NP) with NaBH4 in an aqueous medium. The hierarchically porous carbon monoliths have a plethora of potential applications owing to their mechanical stability and transport properties throughout the monolith. The method of synthesis outlined here can be easily extended to the synthesis of monolithic oxides, such as SnO2, TiO2, ZnO, ITO etc.

Low voltage non-gassing electro-osmotic pump with zeta potential tuned aluminosilicate frits and organic dye electrodes

A novel low-voltage non-gassing electro-osmotic pump using organic-dye electrodes and aluminosilicate frits is demonstrated. Good control of the flow rate is achieved by tuning the zeta potential of the frits in the range of −32.7 mV to −52 mV by varying the aluminum concentration of the aluminosilicate microparticles. The flow rate delivered by the pump is linearly dependent on the zeta potential. The aluminosilicate frits with a maximum zeta potential of −52 mV engendered a maximum flow rate of 27 ± 1.5 μL min−1 V−1 cm−2. In a continuous operation lasting 11 h, the assembled electro-osmotic pump (EOP) can deliver 7.3 mL of a test solution at 60 μA current density. The flow resulted from concerted shifting of protons generated at the anode by electro-oxidation. The consumption of protons at the cathode was accompanied by decomposition of the dye. The non-gassing pump was operated at 0.5 V, which is well below the thermodynamic potential of water electrolysis. The obtained flow rate and pumped volume is sufficient to deliver a bolus of insulin for diabetes management.