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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.

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.

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.

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.

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.

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.

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.

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.

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.