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In this study, a nanocomposite of palladium supported graphene oxide (GO)/metal–organic framework (MOF) was prepared using electroless deposition of Pd on GO followed by impregnation method of Pd@GO and MOF. The prepared materials were characterized with various analytical techniques and their applications as HER electrocatalysts were evaluated using cyclic voltammetry (CV), Tafel plots, and turn over frequencies (TOFs). The HER results showed a radical increment of H2 production in the nanocomposite through the Volmer reaction together with Heyrovsky or Tafel mechanism. This disclosed that the addition of Pd@GO/MOF in the electrolytic system possessed better catalytic characteristics with enhanced current density which may open a new way for hydrogen production and storage via HER.

In recent years, ways to modify the thermodynamic and kinetic properties of functional materials for energy storage have gained an immense interest. One way is through formation of composites by combining two or more compatible materials in the hopes of enhancing properties and superior performance. Surface modification of energy storage materials by coating with transition metals, metal oxides, metal halides and carbon materials has also been exploited with great success. Metal oxides have shown great potential as coating candidates due to their high electric conductivity, ability to enhance structural stability and good electrochemical performance when compared to majority of other surface modifications. In this regard, we review recent advances and various aspects in relation to performance enhancement effects of different metal oxides that are used as coatings on materials for hydrogen adsorption/absorption properties. This review further compares the compatibility of metal oxides on porous and non-porous energy storage materials. Fundamental relationships and the state-of-the art in the prediction of properties and experimental observations are outlined and structure–property-relationships are also discussed.

In this study, a sodium alginate poly(acrylic acid) (SA-poly(AA)) hydrogel and sodium alginate poly(acrylic acid)/zinc oxide (SA-poly(AA)/ZnO) hydrogel nanocomposite (HNC) was synthesized by in situ free-radical polymerization for the sequestration of toxic methylene blue (MB) dye from aqueous solution. The structural properties were analyzed using FTIR, XRD, SEM, TEM, TGA, and DMA The swelling analysis revealed that SA-poly(AA)/ZnO HNC exhibited high water uptake capacity. The kinetics, isotherms, and thermodynamics of adsorption were examined, and results showed that equilibrium data fitted the Langmuir isotherm model, and the adsorption kinetics of MB followed pseudo-second-order model. The maximum adsorption capacity was found to be 1129 mg/g for the SA-poly(AA) hydrogel and 1529.6 mg/g for the SA-poly(AA)/ZnO HNC in 0.25 g/L MB solution at pH 6.0 within 40 min. Thermodynamic parameters for SA-poly(AA) hydrogel and SA-poly(AA)/ZnO HNC substantiated the exothermic and endothermic nature of the adsorption processes, respectively. Moreover, SA-poly(AA)/ZnO HNC presented outstanding reusability with relatively better adsorption efficiencies as compared to SA-poly(AA) hydrogel.

Green synthesis of polypyrrole/nanoscale zero valent iron nanocomposite (Ppy/Fe0 NC) fabricated by a simple in-situ oxidative polymerization method was reported. The structure and the properties of Ppy/Fe0 NC were confirmed using various analytical techniques. The as-prepared Ppy/Fe0 NC was used as an adsorbent for the adsorption of hexavalent chromium (Cr(VI)) through batch experiments. The effect of initial pH, adsorbent dose, contact time, equilibrium concentration and co-existing ions were studied. It was deduced that adsorption data followed the pseudo-second-order rate model and Langmuir isotherm model with a maximum adsorption capacity of 202.02 mg/g at 25°C. Furthermore, high selectivity of Ppy/Fe0 nanocomposite for the removal Cr(VI) was observed even in the presence of co-existing ions. These findings suggest that the green synthesized adsorbent can be used for treatment of wastewater containing Cr(VI).

Carboxymethyl cellulose/poly(acrylic acid) (CMC-cl-pAA) hydrogel and its magnetic hydrogel nanocomposite (CMC-cl-pAA/Fe3O4-C30B) were prepared via a free radical polymerization method and used as adsorbents for adsorption of methylene blue (MB) dye. The samples were characterized using Fourier transform infrared, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy coupled with energy-dispersive X-ray spectrometer, high-resolution transmission electron microscope, and dynamic mechanical analysis. The adsorption performance of the prepared adsorbents was studied in a batch mode. Adsorption kinetics and isotherm models were applied in the experimental data to evaluate the nature as well as the mechanism of adsorption processes. It was deduced that the adsorption followed the pseudo-second-order rate equation and Langmuir isotherm models. The maximum adsorption capacities were found to be 1109.55 and 1081.60 mg/g for CMC-cl-pAA hydrogel and CMC-cl-pAA/Fe3O4-C30B hydrogel nanocomposite, respectively. The adsorption thermodynamic studies suggested that the adsorption process was spontaneous and endothermic for CMC-cl-pAA/Fe3O4-C30B hydrogel nanocomposite. The homogeneous dispersion of the Fe3O4-C30B nanocomposite in the CMC-cl-pAA hydrogel significantly improved the thermal stability, mechanical strength, and excellent regeneration stability. This study demonstrates the application potential of the fascinating properties of CMC-cl-pAA/Fe3O4-C30B hydrogel nanocomposite as a highly efficient adsorbent in the removal of organic dyes from aqueous solution.

Copper(II)phthalocyanine-incorporated metal organic framework (CuPc/MOF) composite material was synthesized for application as an electrocatalyst for hydrogen evolution reaction (HER). The composite exhibited excellent electroactivity compared to the unmodified MOF, as confirmed by the diffusion coefficients (D) values of 3.89 × 10−7 and 1.57 × 10−6 cm2 s−1 for MOF and CuPc/MOF, respectively. The D values were determined from cyclic voltammetry (CV) experiments performed in 0.1 mol L−1 tetrabutylammonium perchlorate/dimethyl sulfoxide (TBAP/DMSO) electrolyte. The Tafel slope determined from the CV data of CuPc/MOF-catalysed HER for 0.450 mol L−1 H2SO4, was 176.2 mV dec−1, which was higher than that of the unmodified MOF (158.3 mV dec−1). The charge transfer coefficients of MOF and CuPc/MOF were close to 0.5, signifying the occurrence of a Volmer reaction involving either the Heyrovsky or the Tafel mechanism for hydrogen generation. For both MOF and CuPc/MOF, the exchange current density (i0) improved with increase in the concentration of the hydrogen source (i.e. 0.033–0.45 mol L−1 H2SO4) Nonetheless, the CuPc/MOF composite had a higher i0 value compared with the unmodified MOF. Thus CuPc/MOF has promise as an efficient electrocatalyst for HER.

The quest for smart sensors with excellent sensitivity, fast response and high reproducibility for hydrogen gas detection has been ongoing for decades. In this work, polyaniline (PANI) was doped with a cobalt-based zeolitic benzimidazolate framework material (CoZIF), to form PANI-CoZIF metal-organic framework (MOF) composite material, which was applied in the electrochemical hydrogen gas sensing. The synthesis of PANI-CoZIF composite was performed by the chemical oxidative polymerization of aniline in the presence of 3.6 wt% CoZIF. The structural properties of the synthesized materials (i.e., PANI, CoZIF, and PANI-CoZIF) were studied by ultraviolet-visible (UV-vis), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman spectroscopic analyses, as well as by thermogravimetric analysis (TGA). Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) and high-resolution transmission electron microscopy/selected area electron diffraction (HR-TEM/SAED) techniques were used for morphological characterization. Both SEM and TEM analyses revealed the grafting of CoZIF on to the surface of PANI in the PANI-CoZIF composite material. XRD patterns and SAED results indicated that PANI and the composite were amorphous in nature. Spectroscopic analyses by FTIR and Raman techniques revealed the coexistence of CoZIF and PANI in the MOF composite material (PANI-CoZIF), which was also confirmed by the high intensities of the characteristic X-ray peaks of ZIF and the polymer. From Tauc plot analysis, it was found that PANI and PANI-CoZIF had band gap energy (Eg) values of 2.5 and 2.3 eV, respectively, indicating that they are both semi-conductors. TGA data confirmed an enhanced thermal stability of PANI-CoZIF compared with pristine PANI. Cyclic voltammetry (CV), chronoamperometry (CA), and Tafel and turn over frequency (TOF) analyses were used to study the electrocatalytic behavior of PANI and PANI-CoZIF in the hydrogen evolution reaction (HER) for gas sensing. There were very significant increases in the TOF value and the magnitude of the catalytic current for PANI-CoZIF compared with pristine PANI as electrocatalysts in the HER. Thus, PANI-CoZIF composite has a greater potential as a suitable electrocatalyst for practical application in the hydrogen fuel technology and hydrogen gas sensing.

Herein, we report on the in-situ chemical polymerization of polyaniline (PANI) doped with zinc-based zeolitic benzimidazolate framework (ZnZIF) to fabricate the PANI-ZnZIF composite for electrochemical hydrogen gas sensing. Fourier-transform infrared and Raman studies of PANI-ZnZIF composite revealed the presence of functional groups corresponding to both ZnZIF and PANI. Both X-ray diffraction and simultaneous thermal analyses showed the co-existence of both PANI and ZnZIF in the composite supported by the decrease in crystallite size and the improvement in the thermal stability, respectively. The scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and selected area electron diffraction revealed that PANI nanofibers wrapped the cube nanofiber-like structures of ZnZIF. The square wave voltammetry, cyclic voltammetry (CV) and chronoamperometry presented good electrochemical performance indicated by an increase in current response with 3 wt% loading of ZnZIF. The high electrochemical current response is due to extraordinary specific surface area, more accessible active sites available for the electrolyte provided by ZnZIF and high conductivity supplied by PANI. Moreover, Tafel parameters and Turnover frequency values derived from CV showed an improvement in the catalytic hydrogen evolution of PANI-ZnZIF composite. The resulting PANI-ZnZIF composite was found to be highly responsive to hydrogen gas as indicated by higher current response and sensitivity (10.8 μA mM H2), faster steady state response time of 4 s accompanied by lower detection limit of 5.27 μM as compared to pure PANI.

Water represents one of the essential resources on earth, and all living organisms rely on it for survival. However, freshwater systems are directly under serious threat by human activities. A recent World Health Organization report has estimated that 2 billion people use contaminated water sources. The major organic contaminants in water bodies include organic dyes. These are directly related to the spread of diseases owing to their allergenic, mutagenic, and carcinogenic characteristics. Dyes occur in the environment through untreated industrial effluents. Also, the advancement in human civilisation cannot be considered without the development of modern industries. However, an attempt to limit the resulting impacts of coloured effluents on global freshwater quality has become the focus of recent research. For this reason, the use of efficient, simple, and low-cost methods for the treatment of dyes-containing industrial wastewater could serve as a useful tool. An effort to meet the demand for “green chemistry” and sustainable development has led to several investigations on polysaccharide-based adsorbents. This chapter exposes a critical discussion on the literature concerning the biopolymeric xanthan gum and kappa-carrageenan polysaccharides as adsorbents for dye removal in an aqueous medium. Functionalisation of these biopolymers through graft copolymerisation and inclusion of inorganic nanoparticles for improved adsorption performance is systematically elaborated.

In the recent years, lithium-ion batteries have prevailed and dominated as the primary power sources for mobile electronic applications. Equally, their use in electric resources of transportation and other high-level applications is hindered to some certain extent. As a result, innovative fabrication of lithium-ion batteries based on best performing cathode materials should be developed as electrochemical performances of batteries depends largely on the electrode materials. Elemental doping and coating of cathode materials as a way of upgrading Li-ion batteries have gained interest and have modified most of the commonly used cathode materials. This has resulted in enhanced penetration of Li-ions, ionic mobility, electric conductivity and cyclability, with lesser capacity fading compared to traditional parent materials. The current paper reviews the role and effect of metal oxides as coatings for improvement of cathode materials in Li-ion batteries. For layered cathode materials, a clear evaluation of how metal oxide coatings sweep of metal ion dissolution, phase transitions and hydrofluoric acid attacks is detailed. Whereas the effective ways in which metal oxides suppress metal ion dissolution and capacity fading related to spinel cathode materials are explained. Lastly, challenges faced by olivine-type cathode materials, namely; low electronic conductivity and diffusion coefficient of Li+ ion, are discussed and recent findings on how metal oxide coatings could curb such limitations are outlined.

The deterioration of hydrogen charging performances resulting from the surface chemical action of electrophilic gases such as CO2 is one of the prevailing drawbacks of TiMn1.52 materials. In this study, we report the effect of autocatalytic Pd deposition on the morphology, structure, and hydrogenation kinetics of TiMn1.52 alloy. Both the uncoated and Pd-coated materials were characterized using scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD). XRD analyses indicated that TiMn1.52 alloy contains C14-type Laves phase without any second phase, while the SEM images, together with a particle size distribution histogram, showed a smooth non-porous surface with irregular-shaped particles ranging in size from 1 to 8 µm. The XRD pattern of Pd-coated alloy revealed that C14-type Laves phase was still maintained upon Pd deposition. This was further supported by calculated crystallite size of 29 nm for both materials. Furthermore, a Sieverts-type apparatus was used to study the kinetics of the alloys after pre-exposure to air and upon vacuum heating at 300 °C. The Pd-coated AB2 alloy exhibited good coating quality as confirmed by EDS with enhanced hydrogen absorption kinetics, even without activation. This is attributed to improved surface tolerance and a hydrogen spillover mechanism, facilitated by Pd nanoparticles. Vacuum heating at 300 °C resulted in removal of surface barriers and showed improved hydrogen absorption performances for both coated and uncoated alloys.

With growth in civilisation and industrialisation, there is an increase in the release of toxic heavy metal ions and dyes into water system, which is of public concern. As a result, appropriate treatment methods have to be implemented in order to mitigate and prevent water pollution. The discovery of nanotechnology has led to the development and utilisation of various nanoadsorbent for the removal of pollutants from water. PANI nanostructures and nanocomposites are noble adsorbents that have gained popularity in addressing water pollution issues and have been reported in literature. In this chapter, the main focus is on the synthesis of PANI nanocomposites and nanostructures and their application as efficient adsorbents for water treatment. Detailed discussions on different synthetic routes and characterisation have been dedicated to applications of these materials and are compared for the adsorptive removal of heavy metal ions and dyes from water.

The current major global crisis is in the sector of water, energy and food security. Due to the growth in civilisation, industrialisation and environmental fluctuations water scarcity and freshwater availability poses major concern to the world, especially to the developing countries. Nearly, one-third of drinkable water is obtained from surface sources such as rivers, dams, lakes, and canals, and some of this water is exposed to contamination. Therefore, appropriate treatment methodologies must be implemented in order to mitigate and prevent water contamination. Photocatalysis is an approach to curb the challenge of water contamination by introducing the use various materials for the degradation of pollutants from wastewater. Metal organic frameworks (MOFs) and their composites as materials of interests have gained popularity in addressing water pollution in photocatalysis applications by acting as absorbents of light, prominent to improve performance of photocatalytic activity. This chapter focuses on the synthesis and characterization of MOFs and their composite materials as efficient photocatalysts for degradation of dyes from wastewater.

The removal of persistent heavy metal ions and recovery of platinum group metals from industrial wastewater continues to be an essential step in safeguarding the available water resources to ensure the safety of humans, animals, and the environment. With adsorption technology being widely implemented due to its cost-effectiveness, metal-organic frameworks (MOFs) have gained popularity owing to their high surface area, porosity, and tunable functionality. MOF-based materials have since been developed for various applications such as catalysis, energy storage, sensing, drug delivery, and recently in water purification. This review gives a background of different synthetic routes available for the preparation of MOFs and also their application in various fields. With more emphasis on the removal of pollutants, MOFs have shown to be efficient in removing organic pollutants and heavy metal ions. Furthermore, potential improvement in the adsorption of heavy metals by MOFs through ion-imprinting technology has emerged as a future field to be explored.

A dye-sensitized solar cell (DSSC) is an unconventional opportunity for silicon solar cells, owing to their flexibility, transparency, and low cost. The necessity for DSSCs to capture more of the sunlight radiation was the motivating force for the fabrication of semiconductor materials based on high surface area. The constituents of DSSC syndicate form a solar cell device. The main components in DSSCs are the conducting substrate, dye, photoanode, catalyst, and electrolyte. The photoanode is a well-known element that generates the energy conversion efficiency. There are different photoanode materials that have been studied to date. Amongst photoanode materials, titanium oxide (TiO2) materials are extensively documented, explored, and considered. In this chapter, effort will be made to survey the strategies to advance the energy efficiency of TiO2-based photoanodes with the introduction of metal-organic frameworks (MOFs) in DSSCs to suppress the recombination rate and electron loss. It was seen that to attain a high conversion yield in DSSCs, it is for very fast collection of produced ion carriers before electron re-combination. This chapter is devoted to the TiO2 and MOF photoanode, their properties, and various improvement approaches.

Exploiting low-cost and efficient electrocatalysts for hydrogen evolution reaction (HER) is an important route to solve the energy crisis and environmental pollution. HER process plays a vital role in many energy storage and conversion systems including water splitting, rechargeable metal–air batteries and the unitised regenerative fuel cells. The platinum-based catalysts are regarded as best electrocatalysts for the HER; nevertheless, they are very exorbitant and scarce. Therefore, it is necessary to develop efficient electrocatalysts based on carbon materials. Graphene oxide (GO), for instance, is a monolayer structure with a high contribution of sp2 hybridised carbon atoms, and various oxygen-containing surface functional groups have attracted the attention of a worldwide research community in the last decades due to its various potential applications linked to the unique combination of properties, such as hardness, physical and chemical stability, high specific surface area, electron mobility and heat transfer. It can be easily manufactured by simple and scalable chemical oxidation approaches from graphite, the reduction of GO into reduced GO (rGO) is a widely used method to obtain graphene. In HER, GO can also be incorporated with metals and porous materials for synergetic effect as co-catalysts for enhancement of electrocatalytic activities. On the other hand, metal–organic frameworks (MOFs) are crystalline materials with porous network structure. They possess various compositions, large surface area, tunable pore structures and are easily functionalised. Recently, MOF‐based electrocatalysts have been rapidly developed with excellent catalytic performance, demonstrating a promising application prospect in HER. In this chapter, the background on hydrogen energy and HER structure, category and synthesis of GO and MOFs are discussed. The application of GO- and MOF-based electrocatalysts for HER is discussed in detail. Their HER parameters such as Tafel slope (b) and exchange current density (i0) are emphatically discussed and followed by the synergetic effect of HER studies of GO/MOF composites as an alternative electrocatalyst for future hydrogen production and storage via HER mechanism.

The current interest in energy storage systems (ESSs) is primarily due to the environmental concerns of the harmful carbon print emissions from the fossil fuels used presently. The development of energy storage systems (ESSs) comes as a crucial factor when it comes to addressing the energy problems arising due to the rapid development of the global economy and the depletion of fossil fuels that brings the increase of environmental pollution. The innovation brought about by the discoveries in nanotechnology on the production of nanostructured materials has driven the rapid growth in the research of novel carbon nanomaterials towards various applications. Through these research efforts, various carbon-based nanomaterials have been discovered to possess unique properties such as high surface area, high electrical conductivity, as well as a range of shapes, sizes and pore-size distributions that are exploited extensively for electrochemical energy storage applications. Supercapacitors (SCs), also called ultracapacitors or electrochemical capacitors, are electrochemical energy storage (EES) devices that store electrical charge on high-surface-area conducting materials. This chapter explores the fundamental electrochemical properties of various nanostructured carbon materials with a great interest based on the synthesis and supercapacitive behaviour of carbon-based nanomaterials such as carbon nano-onions (CNO), carbon nanotubes (CNTs), activated carbon (AC), carbon nanofibres (CNFs), graphene and graphene oxide (GO) and their composites.

There are concerns regarding the depletion of the fossil-fuel resources and the destruction of the environment accompanied with drastic climate changes. Hence, researchers have derived attention on looking for an alternative clean, sustainable renewable, highly efficient energy conversion and storage technologies/systems. The fuel cell is one of the most promising renewable energy source that can provide a stable and constant energy output as long as fuel is supplied continuously. Currently, platinum-based metals are the best electrocatalysts for fuel cells applications. However, due to high cost of platinum, the large-scale synthesis and commercialisation of these electrocatalysts is challenging. Apart from its high cost, the Pt-based electrode also suffers from its susceptibility to time-dependent drift and CO deactivation, and it is unselective. For these reasons, many research groups are developing non-platinum electrocatalysts that are more active, stable and more economical. Carbon-based nanostructured and nanosized materials are widely applied to tackle these demanding challenges associated with energy conversion. Nanostructured carbon-based materials have received interest due to their fascinating physical and chemical properties. They have electronic behaviour ranging from metallic to semiconducting that depends on their structure, composition and chirality. In this chapter, numerous types of carbon nanomaterials such as carbon black, carbon nanofibers, carbon nanotubes and graphenes applied in the electrochemical activity of fuel cells are conversed.

A novel composite of poly(3-aminobenzoic acid) (PABA) and a cobalt zeolitic benzimidazolate framework (CoZIF) has been studied for the production of hydrogen through the hydrogen evolution reaction (HER). The structural characteristics and successful synthesis of PABA, CoZIF and the PABA/CoZIF composite were confirmed and investigated using different techniques. Probing-ray diffraction for phase analysis revealed that the composite showed a decrease and shift in peak intensities, confirming the incorporation of CoZIF on the PABA backbone via in situ polymerization, with an improvement in the crystalline phase of the polymer. The thermal stability of PABA was enhanced upon composite formation. Both scanning electron microscopy and transmission electron microscopy showed that the composite had a rough surface, owing to an interaction between the CoZIF and the external surface of the PABA. The electrochemical hydrogen evolution reaction (HER) performance of the synthesized samples was evaluated using cyclic voltammetry and Tafel analysis. The composite possessed a Tafel slope value of 156 mV/dec and an &alpha, of 0.38, suggesting that the Volmer reaction coupled with either the Heyrovsky or Tafel reaction as the rate determining step. The fabricated composite showed high thermal stability and excellent tolerance as well as high electroactivity towards the HER, showing it to be a promising non-noble electrocatalyst to replace Pt-based catalysts for hydrogen generation.

A novel, modified polypyrrole/m-phenylediamine (PPy&ndash, mPD) composite, decorated with magnetite (Fe3O4) nanoparticles, and prepared via an in-situ oxidative polymerisation, was investigated. The PPy&ndash, mPD/Fe3O4 nanocomposite was employed for the removal of highly toxic oxyanion hexavalent chromium Cr(VI) from an aqueous solution. The structure and successful formation of the PPy&ndash, mPD/Fe3O4 nanocomposite was confirmed and investigated using various techniques. The presence of Fe3O4 was confirmed by high resolution transmission electron microscopy, with an appearance of Fe lattice fringes. The estimation of the saturation magnetisation of the nanocomposite, using a vibrating sample magnetometer, was observed to be 6.6 emu/g. In batch adsorption experiments, PPy&ndash, mPD/Fe3O4 nanocomposite (25 mg) was able to remove 99.6% of 100 mg/L of Cr(VI) at pH 2 and 25 &deg, C. Adsorption isotherms were investigated at different Cr(VI) concentration (100&ndash, 600 mg/L) and temperature (15&ndash, 45 &deg, C). It was deduced that adsorption follows the Langmuir model, with a maximum adsorption capacity of 555.6 mg/g for Cr(VI) removal. Furthermore, isotherm data were used to calculate thermodynamic values for Gibbs free energy, enthalpy change and entropy change, which indicated that Cr(VI) adsorption was spontaneous and endothermic in nature. Adsorption&ndash, desorption experiments revealed that the nanocomposite was usable for two consecutive cycles with no significant loss of adsorption capacity. This research demonstrates the application potential for the fascinating properties of PPy&ndash, mPD/Fe3O4 nanocomposite as a highly efficient adsorbent for the removal of heavy metal ions from industrial wastewater.

Pd-supported copper phthalocyanine/metal organic frameworks (Pd@CuPc/MOF) composite was synthesized by the reaction between CuPc and MOF followed by electroless Pd plating. The structural properties of MOF, Pd@MOF and Pd@CuPc/MOF composite were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), simultaneous thermal analysis (STA), ultraviolet–visible spectroscopy (UV–vis), scanning electron microscopy (SEM/EDS) and Brunauer-Emmett-Teller (BET). The XRD, UV–vis and FTIR analyses showed that Pd was coated on CuPc/MOF composite. SEM and EDS results revealed that Pd nanoparticles were well-dispersed and anchored tightly on the composite. The thermal stability of MOF increased upon addition of Pd and CuPc. The electrochemical hydrogen evolution reaction (HER) performance of the synthesized materials was studied by cyclic voltammetry (CV) and Tafel analysis. The Tafel slope of the composite was 176.9 mV/dec and the transfer coefficient of 0.67 which is close to 0.5. The HER results revealed that the Pd@CuPc/MOF composite has better catalytic characteristic such as high catalytic activity and lowest onset potential compared to MOF. More importantly, the significant enhancement of HER performance at ambient temperature for the composite with Pd content can be ascribed to the hydrogen spillover mechanism in such system.

Polyaniline-metal organic framework (PANI/MOF) composite was prepared by chemical oxidation of aniline monomer in the presence of 3.6 wt% MOF content for hydrogen evolution reaction (HER). The structure, morphology and properties of the fabricated composite were investigated. There was a clear interaction of MOF on the backbone of the PANI matrix through electrostatic interaction as investigated by both Raman and Fourier transform infrared analyses. The MOF exhibited irregular crystals with further wrapping of MOF by PANI matrix as evidenced by both scanning electron microscopy and transmission electron microscopy studies. The PANI composite showed some nanorods and microporous structure. The energy band gap values of PANI and its composite were found to be 1.50 and 1.35 eV, respectively. The thermal stability of the neat PANI increased upon composite formation, which was due to a stabilizing effect of MOF and a change in morphology of the composite. The catalytic effect of MOF, PANI and PANI/MOF composite on HER was studied using exchange current density (i0) and charge transfer coefficient determined by the Tafel slope method. A drastic increase in catalytic H2 evolution was observed in the composite. In addition, the Tafel slope values of PANI and the composite decreased with increasing the concentration of the acid, suggesting the Volmer reaction coupled with either Heyrovsky or Tafel reaction. The i0 increased with increasing the acid concentration and in an order of PANI/MOF > MOF > PANI at various concentrations.

Advanced materials for hydrogen evolution reaction are central to the area of renewable energy. Here, we developed a solvothermal synthesis of metal organic framework (MOF) nanoparticles decorated with poly (3-aminobenzoic acid) (PABA) referred as MOF-3.6 wt.%-PABA and MOF–5 wt.%-PABA composites. The parent material (MOF) and composites were characterized by ultraviolet visible (UV-vis) and Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDS, EDX), selected area electron diffraction (SAED) and cyclic voltammetry (CV). Detailed structural and morphological characterizations established that PABA interacts with MOF on the external surface as observed by appearance of rough surface of the composites. The XRD and SAED showed that MOF and composites are crystalline and the presence of PABA did not alter the crystallinity of the material. Experiments probing the thermal, electrochemical and photophysical properties revealed that the composites were very stable and robust and had exceptionally properties. Significant hydrogen evolution reaction (HER) using CV and Tafel plots, was generated by MOF and composites in dimethyl sulfoxide/tetrabutylammonium perchlorate (DMSO/TBAP) supporting electrolyte in the presence of hydrogen source by applying a negative potential to the electrode.

Electrocatalysis stands as a heart for realization of hydrogen gas (H2) as a source of energy to replace conventional and traditional fossil fuel based energy. In this chapter, we present a comprehensive overview of the state-of-the-art molybdenum disulphide (MoS2) nanostructures for application in electrolytic hydrogen evolution reaction (HER). MoS2 is a crystalline compound consisting of Mo sandwiched between two sulfur atoms and can be identified in four poly-type structures, namely 1T, 1H, 2H and 3R. Firstly, the reaction accompanied with water splitting electrolysis, HER mechanisms as well as parameters to monitor HER reactions are discussed. Furthermore, the chapter describes different types of MoS2 poly-types, chemical synthetic routes and key approaches to activate inert S-containing basal plane of MoS2. This led to superior performance of new materials by combining the advantages of MoS2 components and others. Finally, future integration approaches which can be used to attain MoS2 with exposed edges and excellent electron transport channel are also outlined in this chapter.

Flax fibre was treated with low concentrations of alkali and used to prepare poly(furfuryl alcohol) (PFA)-based composites through in situ polymerization of furfuryl alcohol. The properties of low concentrations of alkali-treated flax fibre and flax fibre–reinforced composites were characterized for their structure and properties by X-ray diffraction, scanning electron microscopy, Fourier transform infrared, thermogravimetric analysis, dynamic mechanical analysis, water absorption and flexural measurements. The alkali-treated flax fibre showed increased cellulose content and crystallinity index with smooth surfaces of the microfibres. PFA composites exhibited dispersed microfibres within PFA matrix with agglomerates. There was also a clear increase in thermal stability, storage modulus and damping factor for all treated PFA composites. Poor resistance to water uptake was also observed for the PFA composites, even though the highest alkali treatment improved the resistance compared to the untreated composite. PFA–flax biocomposites were characterized by improved flexural strength and modulus, except the untreated which showed the opposite.

Lead-doped zinc aluminate (ZnAl 2 O 4 :1.5% Pb 2+ ) spinel nanocrystals powders were prepared by the citric assisted sol-gel process. The effects of annealing temperature (AT) at a fixed dopant concentration on the structure, morphology and optical properties of the powders were investigated. Thermogravimetric analysis (TGA) showed that the minimum annealing temperature required to obtain single phase ZnAl 2 O 4 must be above 400 °C. Fourier transform infrared spectroscopy (FTIR) results suggest that heat treating destroys some of the bonds. From the XRD results, it was observed that the required structure started to grow at the AT of 500 °C. With an increase in AT > 500 °C the structure transformed to single phase of cubic ZnAl 2 O 4 spinel. The crystallinity increases upon further rise of AT to 800 °C. On heating at 600–800 °C, the powders had the average crystallite sizes of around 18–22 nm. Energy dispersive x-ray spectroscopy (EDS) analysis confirmed the presence of the expected elements (Zn, Al, O and Pb). The morphology of the prepared phosphor were influenced by the AT. Transmission electron microscopy (TEM) results revealed that the prepared powders are in the nano-scale range. The band gap of the sample annealed at 800 °C were estimated to be 3.2 eV. The emission position and intensity of the phosphor was dependent on the AT. Emissions arising from both the host and Pb 2+ ion were observed. Emission wavelength of the prepared phosphors can be tuned by varying the AT. The results suggest that ZnAl 2 O 4 :1.5% Pb 2+ is a promising candidate for blue-light emitting phosphor.

The effect of boehmite alumina nanofiller on properties of polylactide/polypropylene blend compatibilized with 3% maleic anhydride grafted polypropylene was investigated. Boehmite alumina nanoparticles were finely dispersed in polylactide/polypropylene/boehmite alumina blend up to 7 wt.% to form blend nanocomposites which were prepared by twin-screw melt compounding. The morphology, thermal, mechanical, heat distortion temperature, thermomechanical and degradation characteristics were investigated. Scanning electron microscopy indicated a tubular morphology with increasing boehmite alumina in the blend matrix particularly at 5 and 7 wt.% of boehmite alumina loadings with few agglomerates. Transmission electron microscopy indicated a highly dispersed boehmite alumina in the blend nanocomposites. Boehmite alumina nanoparticles significantly influenced the thermal properties and a nucleation of the blend matrix. A significant improvement in the tensile modulus and tensile strength upon addition of boehmite alumina in the blend nanocomposites was obtained. However, beyond 3 wt.% of boehmite alumina addition, there was a clear deterioration in mechanical properties.

Water pollution by organic dyes continues to pose a serious health and environmental threat to the ecosystem. Although adsorption using biopolymer-based hydrogels has proven to be an ideal technique for the treatment of these dye contaminants from aqueous solutions, these hydrogels suffer from lack of mechanical stability and recovery as compared to synthetic polymers. Herein, we review the low-cost synthesis of hydrogel incorporated with inorganic components mainly focusing on strategies to improve the mechanical stability and separation of the hydrogel in removing methylene blue (MB) dye from aqueous solution. The literature shows that hydrogel nanocomposites are a class of materials that have flourished significant consideration, especially concerning water treatment. In adsorption technology, hydrogel nanocomposites act as absorbents, prominent to enhance their removal efficiency towards contaminants. This review highlights the preparation and use of hydrogel nanocomposites as efficient adsorbents. In-depth discussions on adsorption and diverse synthetic routes of hydrogels have been devoted to applications of these nanocomposites and are compared in this contribution to the removal efficiency of MB dye from wastewater.

The fundamental properties of supercapacitors (SCs) with descriptions restricted to the metal oxides systems and the effect on the electrochemical performance and synthesis are described in this chapter. Metal oxides such as manganese oxide (MnO), vanadium oxide (V2O5) and ruthenium oxide (RuO) have demonstrated great potential in the field of energy storage due to their structural as well as electrochemical properties, thus attracting huge attention in the past decade and in recent years. The major contributing factor to the electrochemical properties is their capability to achieve relatively high pseudocapacitive performance derived from their theoretical values resulting from their multiple valence state changes. The developments of the metal oxide (MO)-based electrode materials and their composites are being explored from the synthetic point of view as well as their emerging applications as energy storage materials. Therefore, the need to further exploration of MO-based electrodes is motivated by their considerably low-cost and environmentally friendly nature as compared to other supercapacitive electrode materials. This chapter accounts to the overview of various nanostructured metal oxide materials for application as energy storage materials in supercapacitors.

Hydride-forming alloys are currently considered reliable and suitable hydrogen storage materials because of their relatively high volumetric densities, and reversible H2 absorption/desorption kinetics, with high storage capacity. Nonetheless, their practical use is obstructed by several factors, including deterioration and slow hydrogen absorption/desorption kinetics resulting from the surface chemical action of gas impurities. Lately, common strategies, such as spark plasma sintering, mechanical alloying, melt spinning, surface modification and alloying with other elements have been exploited, in order to overcome kinetic barriers. Through these techniques, improvements in hydriding kinetics has been achieved, however, it is still far from that required in practical application. In this review, we provide a critical overview on the effect of mechanical alloying of various metal hydrides (MHs), ranging from binary hydrides (CaH2, MgH2, etc) to ternary hydrides (examples being Ti-Mn-N and Ca-La-Mg-based systems), that are used in solid-state hydrogen storage, while we also deliver comparative study on how the aforementioned alloy preparation techniques affect H2 absorption/desorption kinetics of different MHs. Comparisons have been made on the resultant material phases attained by mechanical alloying with those of melt spinning and spark plasma sintering techniques. The reaction mechanism, surface modification techniques and hydrogen storage properties of these various MHs were discussed in detail. We also discussed the remaining challenges and proposed some suggestions to the emerging research of MHs. Based on the findings obtained in this review, the combination of two or more compatible techniques, e.g., synthesis of metal alloy materials through mechanical alloying followed by surface modification (metal deposition, metal-metal co-deposition or fluorination), may provide better hydriding kinetics.

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Cellulose/poly(furfuryl alcohol) (PFA) composites were prepared via in-situ polymerization process using p-toulene sulfonic acid as a catalyst. Cellulose was extracted from cotton fibers using chemical treatments with basic media of NaOH, NaClO2 and KOH. Acid hydrolysis at different concentrations (30, 40 and 50%) of sulphuric acid was used and the final suspended cellulose was incorporated in PFA. The treatments of the cotton fibers ensued to higher crystalline cellulose which was proportional to sulphuric acid contents. Scanning electron microscopy studies (SEM) results showed a poor interfacial interaction when 50% acid content was used for hydrolyses. The effect of fiber reinforcement on thermal and dynamic mechanical properties of the composites was investigated using thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMTA). The TGA results showed higher thermal stability of cellulose/PFA composites as compared to the neat PFA. The DMA results showed that the incorporation of the cellulose fibers imparts significant enhancement in the storage modulus of the PFA matrix. There was also the clear decrease in intensity of the tan peak of the composites compared to the neat PFA. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

A novel hybrid-hybrid nanocomposite based on 4-tetranitro copper(II)phthalocyanine (TNCuPc) grown on metal organic frameworks (MOF) as a noble metal-free catalyst for hydrogen evolution reaction (HER) was developed by a simple impregnation method. The structure, surface area and the morphology of the bare MOF, TNCuPc and the TNCuPc/MOF composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, Brunauer-Emmet-Teller, scanning electron microscopy, transmission electron microscopy and simultaneous thermal analysis. The electrocatalytic activity of the samples towards the HER was evaluated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry, exchange current density, i0, Tafel slope value, b, as well as charge transfer coefficient, α. The spectroscopic analyses indicated a successful synthesis of TNCuPc and its composite. The morphological results showed the development of rod-like structures of TNCuPc on the surface of the MOF. The composite exhibited an onset potential of about −0.713 V vs. Ag/AgCl in 0.1 M TBAP/DMSO and 0.3 M H2SO4 solutions, which is 44 mV and 9 mV more positive than that of MOF and TNCuPc respectively. The composite showed the rate determining step (RDS) to be the Volmer reaction in conjunction with either Heyrovsky or Tafel reaction as the RDS due to the Tafel slope value of 147 mV/dec and an α of 0.4. The i0 value of the TNCuPc/MOF composite was about 1.6 times that of the bare MOF. The EIS results showed the charge transfer resistance (Rct) of 12.6 kΩ for the TNCuPc/MOF composite as compared to MOF and TNCuPc values of 41 and 18.6 kΩ, respectively, demonstrating an excellent conductivity of the composite. In addition, Rct values of materials follow the sequence, blank

Polyaniline-based metal-organic framework (PANI/MOF) composite was synthesized by chemical oxidation of aniline monomer in the presence of MOF content for practical usages as effective hydrogen production. PANI and composite were characterized by ultraviolet visible (UV-vis) and Fourier transform infrared (FTIR) spectroscopy, atomic absorption spectroscopy (AAS), powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDS, EDX), selected area electron diffraction (SAED) and cyclic voltammetry (CV). Detailed structural and morphological characterizations established that PANI is wrapping MOF. The XRD, Raman and FTIR analyses showed that MOF was incorporated on the backbone of PANI through electrostatic interactions. This was supported by AAS analysis, revealing the amount of copper metal present in the composite. The determined energy band gap of the composite was in good agreement with previously reported catalysts for hydrogen evolution reaction (HER). Experiments probing the thermal, electrochemical, HER and photophysical properties revealed that the composite was very stable and robust and had exceptionally properties. Significant HER was generated by the composite in dimethyl sulphoxide/tetrabutylammonium perchlorate (DMSO/TBAP) supporting electrolyte in the presence of hydrogen source by applying a negative potential to the electrode. PANI and MOF also generated a weak HER as compared to composite.

Biocomposites containing ultraviolet (UV) radiation absorbing inorganic nanofillers are of great interest in food packaging applications. The biodegradable polylactide (PLA) composite films were prepared by solvent casting method by incorporating 1 wt % of titanium dioxide (TiO2) and Ag-TiO2 (silver nanoparticles decorated TiO2) nanoparticles to impart the photodegradable properties. The films were exposed to UV radiation for different time periods and morphology of the composite films before and after UV exposure were investigated. The results showed that homogenous filler distribution was achieved in the case of Ag-TiO2 nanoparticles. The thermal properties and thermomechanical stability of the composite film containing Ag-TiO2 nanoparticles were found to be much higher than those of neat PLA and PLA/TiO2 composite films. The scanning electron microscopy and X-ray diffraction studies revealed that the photodegradability of PLA matrix was significantly improved in the presence of Ag-TiO2 nanoparticles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013