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High-temperature treatment increased the conductivity, carrier density and mobility of N-RGO. Inclusion of PANI tailored activities from capacitive to battery-like and diffusion-controlled.

This study evaluated the electrochemical performance of cellulose-based multiwalled carbon nanotubes (MWCNTs) as electrode materials. MWCNTs were subsequently treated with acid, heat, N,N′-dimethylformamide and ferrocene carboxaldehyde to obtain the following samples; a-MWCNTs, t-MWCNTs, DMF-MWCNTs and Fc-MWCNTs, respectively, with the samples isolated at each step. The techniques employed to study the physicochemical properties of the MWCNT samples were transmission and scanning electron microscopes, X-ray photoelectron spectroscopy, thermal gravimetric analysis, cyclic voltammetry, electrochemical impedance spectroscopy, nitrogen sorption analysis and Raman and Fourier transform infrared spectroscopies. The electrochemical properties of the four materials were tested by combining them with Nafion and casting them onto a Pt electrode that formed the working electrode of a three-electrode cell with Ag/AgCl as a reference electrode and a Pt counter electrode. The background electrolyte was 1 M Na2SO4. The a-MWCNTS contained the highest concentration of carboxylic oxygen moieties and resulted in an enhanced specific capacitance ( $${C}_{s}$$ ) of 42 F g−1 with the smallest voltage window of 0.30 V. The DMF-MWCNTs and t-MWCNTs had the most stable cycle stabilities and enhanced kinetic response of the electrochemical current. The Fc-MWCNTS exhibited the broadest capacitive voltage window of 0.80 V against an Ag/AgCl reference electrode, the highest specific energy density of 2.70 Wh kg−1 and the second highest $${C}_{s}$$ of 30 F g−1. The treatment protocols demonstrate material tailoring strategies that enable a comparison of the effect of carboxylic acid, phenolic and lactone moieties on MWCNTs and the resulting associated specific energy density, kinetic response, diffusion path length, cycle life and operational voltage window of the electrode material in electrochemical capacitors.

This study entails a theoretical investigation of the effect of the hole transport layer (HTL) and electron transport layer (ETL) materials on a lead-free perovskite solar cell based on methylammonium tin iodide (CH3NH3SnI3). The simulations of the solar cells were conducted with the aid of the one-dimensional solar cell capacitance simulator, SCAPS-1D. The initial primary cell with the following architectural design: glass/FTO/WS2/CH3NH3SnI3/P3HT/Au, was simulated to yield a modest power conversion efficiency (PCE) of 10.47%. In an attempt to improve the PCE of this device, several materials were tested as the HTL, and their effects on the PCE were simulated. Subsequently, various ETL materials were tested with what were found to be the best possible HTL materials. The PCE of the primary device increased from 10.47% to over 16% with the utilization of 2,2′,7,7′-tetrakis [N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD), copper(I) oxide (Cu2O), copper(I) thiocyanate (CuSCN), copper(I) iodide (CuI), and poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno-[3,2-b]thiophene) (D-PBTTT-14) as HTLs. Tungsten disulfide (WS2) was shown to be the best suitable ETL material. The density of defects of the absorber for the devices with tungsten disulfide as the ETL and Cu2O, D-PBTTT-4, CuSCN, spiro-OMeTAD, and CuI as the HTLs, was best at 1.5 × 1017 cm−3, while for the primary device, the best value of the density of defects was 1.5 × 1014 cm−3. Furthermore, the energy barriers at the interface for primary and optimum devices was examined. Additionally, the effect of the external operating temperature on the performance of the devices was investigated. The simulation results allow one to propose the best HTL and ETL materials for high performance of lead-free perovskite solar cells, based on tin.

Graphitic carbon nitride (g-C3N4) is a metal-free photoactive material which has gained significant interest in the advancement of electronic and optical devices because of its attractive optoelectronic properties, such as tuneable band gap, and suitable chemical and thermal stability. This material has been utilized in a range of applications including photocatalysis, biosensing and photovoltaics. Bulk g-C3N4 (B-g-C3N4) has been shown to exhibit low photo-efficiency due to its low specific surface area and high rate of recombination of photo-generated charges; thus, there is a need for its exfoliation. Also, the type of exfoliation method utilized is crucial. In this work, two exfoliation methods of g-C3N4, namely, liquid and thermal etching exfoliation, were investigated. Both methods successfully produced g-C3N4 nanosheets, but those synthesized by liquid exfoliation (CNNS-LE) had a much larger specific surface area of 41.68 m2 g−1 than those prepared by thermal exfoliation (CNNS-TE) (14.76 m2 g−1) or the parent B-g-C3N4 (3.22 m2 g−1). The band gap energies of B-g-C3N4, CNNS-LE and CNNS-TE were found to be 2.71, 2.59 and 1.89 eV, respectively. Graphitic carbon nitride nanosheets prepared by thermal exfoliation (CNNS-TE) were found to be 2.5 times more effective in the photo-degradation of Rhodamine B than B-g-C3N4 and CNNS-LE. This is attributed to the positive effect of their porous structure, which gives rise to effective separation of charges, and their extended light absorption properties. Thus, thermal treatment introduces structural defects and electronic modifications that result in an enhanced photocatalytic performance. Consequently, thermal etching is effective in exfoliation of B-g-C3N4 to form a material suitable for photo-driven applications.

Graphitic carbon nitride (g-C3N4) has become an important material because of its attractive optoelectronic properties. It has been applied in various fields such as photovoltaics, biosensi...

The design and fabrication of electronic devices based on graphene nanomaterials are dependent on the tuning of Fermi levels. This can be achieved by doping graphene oxide (GO) with an electron-withdrawing (p-type) or electron-donating (n-type) species that causes changes in the electron density and enhances the electrochemical properties. In this research, the effect of boron content on the optical, electrochemical, and conductivity properties of GO was investigated. Boron-doped reduced graphene oxide (B-rGO) was synthesized via a chemical vapor deposition method by using GO and varying amounts of boric anhydride, as a boron precursor, at a doping temperature of 600 °C. The B-rGO samples were characterized by standard spectroscopic techniques. B-rGO had a sheet structure with various graphene islands and disordered regions. The highest boron content incorporated into the reduced GO framework was 7.12%. B-rGO samples manifested strong absorption in the ultraviolet region. An electronic band structure with a low charge resistance of 20.23 Ω and enhanced electrical conductivity properties of 5.920 S cm−1 was observed and noted to be dependent on the concentration of boron incorporated. All the B-rGO samples demonstrated a p-type conductivity behaviour which is attributed to an increase in the density of states near the Fermi level. This work opens a new avenue for the fabrication of solar cells based on p-type B-rGO.

Due to the finite nature, health and environmental hazards currently associated with the use of fossil energy resources, there is a global drive to hasten the development and deployment of renewable energy technologies. One such area encompasses perovskite solar cells (PSCs) that have shown photoconversion efficiencies (PCE) comparable to silicon-based photovoltaics, but their commercialisation has been set back by short-term stability and toxicity issues, among others. A tremendous potential to overcome these drawbacks is presented by the emerging applications of graphene derivative-based materials in PSCs as substitutes or components, composites with other functional materials, and enhancers of charge transport, blocking action, exciton dissociation, substrate coverage, sensitisation and stabilisation. This review aims to illustrate how these highly capable carbon-based materials can advance PSCs by critically outlining and discussing their current applications and strategically identifying prospective research avenues. The reviewed works show that graphene derivatives have great potential in boosting the performance and stability of PSCs through morphological modifications and compositional engineering. This can drive the sustainability and commercial viability aspects of PSCs.

Carbon nanostructured materials (CNMs) have vast capability in the field of energy, for storage and conversion purposes. Consequently, extensive greener and environmentally benign synthesis techniques that employ natural and readily renewable, low-cost waste materials need to be established. Herein, cellulose is considered as an alternative precursor source for the synthesis of CNMs. In the past decade, ionic liquids (ILs) have exhibited a great potential in a diverse number of applications. However, insignificant attention has been paid to the structure of ILs in relation to their extended application as a media for the dissolution of cellulose to avail carbon for CNMs synthesis. As baseline, a number of ionic liquids were used as carbon sources for CNM production, and distinct differences were found, depending on the type of ionic liquid used and the temperature of synthesis. Furthermore. CNMs were fabricated using a combination of the ionic liquid, 1-butyl-3-methylimidazolium chloride, [C4MIM]Cl, and cellulose, in the presence of ferrocene as catalyst precursor, using the floating catalyst chemical vapour deposition technique. Typical spaghetti like, hollow tubular structures with bamboo compartments, resembling N-doped multiwalled tubular carbon nanomaterials were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) respectively. Thermal stability studies showed thermogram profiles with a stability of around 550 °C. The sample synthesised with cellulose was more stable than the sample synthesised from IL and ferrocene only. Characteristic D- and G-bands were observed around 1380 and 1560 cm−1, respectively, for Raman spectroscopy. X-ray diffraction (XRD) showed characteristic tubular carbon nanomaterials and or graphitic/N-graphitic diffraction patterns.

Presented herein is the nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) production from a residue, sugarcane bagasse, using 1-butyl-3-methylimidazolium chloride [C4MIM]Cl as the solvent and nitrogen source, and ferrocene as the catalyst source. N-MWCNTs were synthesised using the floating catalyst chemical vapour deposition method at 850 °C. The synthesised N-MWCNTs were characterised using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), X-ray diffraction (XRD) spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. Hollow tubular structures of N-MWCNTs were observed using TEM. These observations correlated morphology from SEM which showed spaghetti-like structures, and also EDS detected the presence of nitrogen. Raman spectroscopy indicated MWCNT bands, around 1350 and 1580 cm−1 assigned to D-band and G-band due to defective and graphitic carbon vibrations, respectively. Also, XRD patterns showed typical N-MWCNT structures with a strong intensity peak at 2θ = 26.4° which was indexed as the C(002) reflection of graphite. TGA showed an N-CNTs thermogram curve, with the main decomposition temperature around 590 °C. The study showed that N-MWCNTs were successfully synthesised from sugarcane bagasse. The study significantly establishes a strategy for utilisation and value addition of a residue which is abundant from sugar production mills.

Photovoltaics is a portentous alternative to the nonrenewable energy resources. Organic solar cells (OSCs) offer several advantages over inorganic counterparts in terms of low-cost device productio...

Solventless grinding of 2-aminophenol and the corresponding aldehyde furnished compounds 2-(pyridin-2-ylmethylene)aminophenol (L1), 2-(pyridin-4-ylmethylene)aminophenol (L2), 2-(thiophen-2-ylmethylene)aminophenol (L3) and 2-(furan-2-ylmethylene)aminophenol (L4), in excellent yields of 97–99%. Reaction of ligands L1–L4 with zinc or magnesium alkyl solutions produced complexes [Mg(L1)2] (1), [Mg(L2)2] (2), [Mg(L3)2] (3) and [Mg(L4)2] (4) or [Zn(L1)2] (5), [Zn(L2)2] (6), [Zn(L3)2] (7) and [Zn(L4)2] (8). The complexes were characterized by 1H NMR, 13C NMR and IR spectroscopies, elemental analysis and mass spectrometry. Complexes 1 was further analysed by single-crystal X-ray crystallography. The complexes were investigated as catalysts/initiators in the ring-opening polymerization (ROP) of e-caprolactone (e-CL), ʟ-lactide (ʟ-LA) and rac-lactide (rac-LA). Mg(II) complexes 1–4 (kapp = 0.12–0.58 h−1) were more efficient catalyst as compared to the Zn(II) complexes 5–8 (kapp = 0.04–0.24 h−1). The catalytic activity was enhanced by adding of alcohol co-initiators. Comprehensive kinetic and mechanistic investigations revealed that the polymerization reaction follows pseudo-first-order kinetics. Moderate molecular weights increased from 1234 to 4567 g mol−1 with an increase in catalyst concentration with polydispersity (PDIs) ranging from 1.4 to 2.0. The enthalpy ΔHp were found to be 23.5 and 63.9 kJ mol−1 while the entropy of activation (ΔSp) values were −157 and −33 JK−1 mol−1 for e-CL and ʟ-LA monomers, respectively.

The ongoing research toward meeting global energy demands requires novel materials from abundant renewable resources. This work involves an investigation on nitrogen-doped carbon nanotubes (N-CNTs) synthesized from relatively low-cost and readily available biomass as carbon precursors and their use as electrodes for supercapacitors. The influence of the ionic liquid 1-butyl-3-methylimidazolium chloride, or its combination with either sugarcane bagasse or cellulose (IL-CNTs, ILBag-CNTs, and ILCel-CNTs, respectively), in the synthesis of N-CNTs and the resultant effect on their physical and electrochemical properties was studied. Systematic characterizations of the N-CNTs employing transmission electron microscopy (TEM), thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), elemental analysis, nitrogen sorption analysis, cyclic voltammetry, and electrochemical impedance spectroscopy were performed. TEM data analysis showed that the mean outer diameters decreased, in the order of IL-CNTs &gt, ILBag-CNTs &gt, ILCel-CNTs. The N-CNTs possess only pyridinic and pyrrolic nitrogen-doping moieties. The pyridinic nitrogen-doping content is lowest in IL-CNTs and highest in ILCel-CNTs. The N-CNTs are mesoporous with surface areas in the range of 21–52 m2 g−1. The ILCel-CNTs had the highest specific capacitance of 30 F g−1, while IL-CNTs has the least, 10 F g−1. The source of biomass is beneficial for tuning physicochemical properties such as the size and surface areas of N-CNTs, the pyridinic nitrogen-doping content, and ultimately capacitance, leading to materials with excellent properties for electrochemical applications.

Introduction The aggressive search for renewable energy resources and essential pyrosynthetic compounds has marked an exponential rise in the thermal degradation of biomass materials. Consequently, clean and sustainable transport fuels are increasingly desirable in a highly industrialized economy, for energy security and environmental protection. For this reason, biomass materials have been identified as promising alternatives to fossil fuels despite the challenges resulting from the possible formation of toxic nitrogen-based molecules during biomass degradation. In order to understand the free radical characteristic challenges facing the use of bio-oil, a brief review of the effects of free radicals in bio-oil is presented. Methodology Pyrolysis was conducted in a tubular flow quartz reactor at a residence time of 2 s at 1 atm. pressure, for a total pyrolysis time of 5 min. The thermal degradation of biomass components was investigated over the temperature range of 200 to 700 °C typically in 50 °C increments under two reaction conditions; pyrolysis in N2 and oxidative pyrolysis in 5% O2 in N2. The pyrolysate effluent was analysed using a Gas chromatograph hyphenated to a mass selective detector (MSD). Results The yield of levoglucosan in the pyrolysis of cellulose in the entire pyrolysis temperature range was 68.2 wt % under inert conditions and 28.8 wt % under oxidative conditions. On the other hand, formaldehyde from pyrolysis of cellulose yielded 4 wt % while that from oxidative pyrolysis was 7 wt % translating to ⁓ 1.8 times higher than the yield from pyrolysis. Accordingly, we present for the first time dioxin-like and dibenzofuran-like nitrogenated analogues from an equimassic pyrolysis of cellulose and tyrosine. Levoglucosan and formaldehyde were completely inhibited during the equimassic pyrolysis of cellulose and tyrosine. Conclusion Clearly, any small amounts of N-biomass components such as amino acids in cellulosic biomass materials can inhibit the formation of levoglucosan–a major constituent of bio-oil. Overall, a judicious balance between the production of bio-oil and side products resulting from amino acids present in plant matter should be taken into account to minimize economic losses and mitigate against negative public health concerns.

Environmental pollution has been a challenging phenomenon in most developing countries, due to the weak enforcement of environmental regulations. As a result, humans and animals are exposed to different environmental pollutants, which threaten their very existence. Some of the emerging pollutants of great concern are polybrominated diphenyl ethers (PBDEs) since they are categorized as probable human carcinogens and are also known to bioaccumulate in fatty tissues of animals and humans, reaching toxic levels upon continued exposure. Monitoring of these pollutants is therefore paramount as it contributes to addressing the problem of human exposure and environmental pollution. Their monitoring involves sample preparation methods followed by quantification with various detection techniques. Sample preparation methods that aim at reducing matrix interferences, enriching analytes and transfer of analytes to a desirable solvent, have evolved from conventional methods to advanced methods that facilitate the detection of these chemicals at very low concentrations. Likewise, detection techniques have advanced from chromatographic detection techniques to miniaturized systems that involve sensors. This chapter discusses PBDEs as emerging pollutants, their sources, and toxicological implications on humans, as well as advances in sample preparation methods and detection techniques in the determination of PBDEs.

Presently, artemisinin-based combination therapy (ACT) is the first-line therapy of Plasmodium falciparum malaria. With the emergence of malaria parasites that are resistant to ACT, alternative antimalarial therapies are urgently needed. In line with this, we designed and synthesised a series of novel N-(7-chloroquinolin-4-yl)-N’-(4,6-diphenylpyrimidin-2-yl)alkanediamine hybrids (6a-7c) and evaluated their inhibitory activity against the NF54 chloroquine-susceptible strain as a promising class of antimalarial compounds. The antiplasmodial screening revealed that seven analogues showed promising to good activity with half-maximal inhibitory concentration (IC50) = 0.32 μM–4.30 μM. Compound 7a with 1,4-diamine butyl linker and 4-hydroxyl phenyl on fourth and sixth position of pyrimidine core showed the most prominent activity with an IC50 value of 0.32 ± 0.06 μM, with a favourable safety profile of 9.79 to human kidney epithelial (HEK293) cells. The remaining six analogues showed moderate activity with IC50 values ranging from 7.50 μM to 83.01 μM. We further investigated the binding affinities of the molecules to two essential cytosolic P. falciparum heat shock protein 70 homologues; PfHsp70-1 and PfHsp70-z. Compound 7a exhibited the highest binding affinity for both PfHsp70s with KD in a lower nanomolar range (4.4–11.4 nM). Furthermore, molecular docking revealed that compounds 6, 6k, 7b and 7a exhibited better fitness in PfHsp70-1 with compound 7a showing the highest and lowest binding scores of −9.8 kcal/mol. Therefore, we speculate that PfHsp70-1 is one of the targets of these inhibitors. The bioisoteric replacement of the groups at phenyl ring at the fourth and sixth position of the pyrimidine core had a constructive association with antiplasmodial activity. The promising antiplasmodial activity of the synthesised analogues illustrates how crucial molecular hybridisation is as a strategy in the development of quinoline-pyrimidine hybrids as prospective antiprotozoal agents.

In the past few years, dye-sensitized solar cells (DSSCs) have received considerable research attention, as potential alternatives to the commonly used, but expensive, silicon-based solar cells owing to the low-cost, facile fabrication procedures, less impact on the environment, capability of working even under low incoming light levels, and flexibility of DSSCs. However, the relatively low power conversion efficiencies (PCEs) and poor long-term operational stability of DSSCs still limit their large-scale and commercial applications. As a consequence, this has prompted tremendous research effort towards the realization of high performance and sustainable devices, through tailoring of the properties of the various DSSC components, via approaches such as introducing novel materials and new synthesis techniques. Among these, the application of novel materials, especially carbon-based materials, such as graphene and its derivatives, is more appealing due to their excellent optoelectronic, mechanical, thermal and chemical properties, which give them ample potential to replace or modify the traditional materials that are commonly used in the fabrication of the various DSSC components. In addition, the low-cost, abundance, non-toxicity, large specific surface area, flexibility and superior stability of graphene-based materials have enabled their recent use as photoanodes, i.e., transparent conducting electrodes, semiconducting layers and dye-sensitizers, electrolytes and counter electrodes in DSSCs. Recently, the introduction of graphene-based materials into DSSCs resulted in a pronounced increase in PCE from ∼0.13 to above 12.00%. Thus, employing the recent breakthroughs can further improve the optoelectronic properties of the various DSSC components and, hence, close the gap between DSSCs and their silicon-based counterparts that are currently exhibiting desirable PCEs of above 26%. Therefore, this review focuses on the recent applications of graphene-based materials as photoanodes, electrolytes and counter electrodes, for the possible fabrication of all-carbon-based DSSCs. The limitations, merits and future prospects of graphene-based DSSCs are discussed, so as to improve their photovoltaic performance, sustainability and cost-effectiveness.

Considering its availability, renewable character and abundance in nature, this review assesses the opportunity of the application of biomass as a precursor for the production of carbon-based nanostructured materials (CNMs). CNMs are exceptionally shaped nanomaterials that possess distinctive properties, with far-reaching applicability in a number of areas, including the fabrication of sustainable and efficient energy harnessing, conversion and storage devices. This review describes CNM synthesis, properties and modification, focusing on reports using biomass as starting material. Since biomass comprises 60–90% cellulose, the current review takes into account the properties of cellulose. Noting that highly crystalline cellulose poses a difficulty in dissolution, ionic liquids (ILs) are proposed as the solvent system to dissolve the cellulose-containing biomass in generating precursors for the synthesis of CNMs. Preliminary results with cellulose and sugarcane bagasse indicate that ILs can not only be used to make the biomass available in a liquefied form as required for the floating catalyst CVD technique but also to control the heteroatom content and composition in situ for the heteroatom doping of the materials.