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In this study, porous carbon has been prepared through potassium hydroxide (KOH) activation of coconut fiber (CF) and subsequent carbonization in the presence of an inert gas. The activated carbons (AC) were prepared via carbonization of the precursor at different temperatures. Subsequently, their electromagnetic wave absorption (EMWA) performance was investigated at X-band frequency. The phase crystallinity, porous features, and degree of graphitization of the activated carbons were studied using XRD, nitrogen adsorption/desorption isotherm, and Raman spectroscopy, respectively. Using the BET method, the activated carbon prepared at 750 °C displayed a high specific surface area of 602.9 m2 g−1 and an average pore size of 6 nm, which confirms the extant of mesopores. The EMWA was studied using COMSOL Multiphysics software based on the finite element method. Results show that the activated carbon prepared at 750 °C attained an optimal reflection loss of −45.6 dB at 10.96 GHz with a corresponding effective bandwidth of 3.5 GHz at a thickness of 3.0 mm. In conclusion, this study interestingly shows that porous carbon obtained from coconut fiber has great potential for attenuating electromagnetic waves.

Abstract: The investigation of a Dye-Sensitized Solar Cell (DSSC) as an alternative approach to the conventional photovoltaic cell (silicon-based) is attracting remarkable attention recently. This stems from the excellent optical properties of graphene, such as impressive transparency, conductance in near-infrared and visible light spectrums, along with its thermochemical stability, as reported in the literature. However, the main limitation of graphene production is the lack of suitable methods for its industrial-scale synthesis. Consequently, the research on industrial applications of graphene development and understanding of how to pragmatize existing theoretical approaches are still ongoing in the related research domain. This is exemplified in single, few, and adhesive layer mechanical cleavage graphene methods, which are not yet practicable, as these methods will restrict the chance for scaling up. These limitations and inadequate reviews on graphene development impelled the authors to compile the advances in graphene synthesis, properties, recent applications, and future directions. The mechanical exfoliation synthesis technique delivers quality graphene films sized from 5 to 10 μm. Graphene-TiO2 hybridization was also found to possess efficiency acclivity as high as 39%. This review provides significant implications for a better understanding of graphene performance indicators and insight for future research in photovoltaic or optical modulation devices.

This work assessed the effect of plasmonic green synthesized silver nanoparticles (AgNPs) dispersed in Titanium dioxide (TiO2) nanoparticles on the efficiency of DSSC. Natural plant extracts from air-dried Neem (Azadirachta indica) and Henna (Lawsonia inermis) leaves were used as sensitizers with commercially available Ruthenium dye (N719). The optical absorption band obtained at 425 nm confirmed the presence of the AgNPs and incorporating the AgNPs into TiO2 and dye loading increased the absorbance significantly. The optical band gap results showed that the energy gap decreased as the absorbance increased. The DSSC sensitized by N719 dye offered the highest conversion efficiency of 4.09%, followed by 1.57% by Neem extract and 1.18% by Henna extract. It was shown from the results that natural plant extracts as sensitizers and plasmonic green synthesized AgNPs incorporated into TiO2 as the photoanode are good materials for the fabrication of DSSC with outstanding environmental friendliness.

Recently, the conversion of palm waste to activated carbon for various applications has attracted significant attention from researchers. Over the years, abundant palm wastes have been generated due to active palm milling in various part of the world. These environmentally challenging wastes have been converted to valuable and economical materials for gas adsorption and water treatment but rarely for energy storage application. The lignocellulose composition of palm wastes has made it a favorable candidate for starting material of activated carbon for supercapacitor application. In this review, the pretreatment condition, factors to consider for choosing starting material, activation techniques, and activation parameters such as activation temperature, activation time, activation agent and impregnation ratio are analyzed. The advantages of the synergistic effect of the lignocellulose composition of different palm wastes for energy storage device is discussed. The major drawbacks in the conventional Barrett-Joiner-Halenda (BJH) porosity characterization technique are addressed and the novel Non-localized Density Functional Theory characterization technique is suggested. Conclusively, future prospects in the activation of palm bio-wastes for supercapacitor application are highlighted.

In this study, we have evaluated the effect of various solvents for natural dye extraction and suitable sensitization of the same extracted dye on mesoporous TiO2 for dye sensitized solar Cell (DSSC) applications. Twelve different extraction solvents, namely, distilled water, ethanol, acetone, methanol, acetonitrile, dimethyl sulfoxide (DMSO), chloroform, n-hexane, ethyl acetate, toluene, dichloromethane (DCM) and isopropanol were employed to extract natural dyes from Punica granatum (pomegranate) peels, Citrus reticulata (tangerine) peels and Parquetina nigrescens (African parquentina) leaf. The polar solvents like; distilled water, methanol and ethanol were found to perform best to extract betacyanin dye from Punica granatum peels while the non-polar solvents like; dichloromethane and chloroform extract the most carotenoid and chlorophyll from Citrus reticulata peels and Parquetina nigrescens leaf, respectively. The natural dye extraction process was analyzed using UV–vis and photoluminescence spectroscopy. Further the extracted dye sensitization over TiO2 was monitored with solvent dependent surface wettability chemistry using contact angle measurements. The best dye adsorption solvent was achieved from using distilled water, acetone and dichloromethane for Punica granatum, Citrus reticulata and Parquetina nigrescens dyes, respectively.

Agricultural waste-derived absorbers have drawn extensive attention in electromagnetic wave absorption owing to their unique advantages such as good carbon content and porosity. In this study, porous activated carbon (PAC) was derived from banana peel via chemical activation and carbonization at different temperatures. Then, Co3O4@PAC composites were prepared using the facile hydrothermal method. The thermal stability, phase crystallinity, chemical composition, surface morphology, and porosity of the samples were studied using TGA, XRD, FTIR, XPS, FESEM, and SAP characterization techniques, respectively. Co3O4@PAC700 composite with a cornales flower-like morphology achieved an optimum reflection loss (RL) of −44.50 dB at 2.0 mm thickness. Likewise, Co3O4@PAC600 showed an optimum RL value of −51.50 dB at 11.39 GHz with a matching thickness of 2.5 mm. The magnetic loss, interfacial polarization, porous flower-like structure, and conduction loss contributes adequately towards the superior absorption performance of Co3O4@PAC composites at X-band frequency. The unique flower-like morphology of the composites with good porosity would favour EM wave scattering and multiple reflections of EM wave, thereby resulting in high attenuation of the EM wave. The flower-like morphology prolongs the electromagnetic wave propagation path which would favour gradual attenuation of the electromagnetic wave. This work suggests that the Co3O4@PAC composites can be considered as a promising absorber for EM absorption application. This study provides a new path to designing novel magnetic and dielectric composite for effective microwave absorption.

First principle calculation was performed to investigate material properties such as structural, electronic, mechanical and thermoelectric of ATiO3 (Be, Mg, Ca, Sr or Ba) a perovskite based oxide within density functional theory. Calculations were performed using PBEsol exchange correlation functional within generalized gradient approximation (GGA). Structural and electronic properties were elaborated since their effect gives information about the thermoelectric performance. The underestimate of band gap from DFT calculation were corrected by using DFT with Modified Becke and Johnson (mBJ). It was observed that compound with small band gap have higher electrical conductivity and at the same time, high performance of thermoelectric power factors. BeTiO3 was found to possess very low power factor due to its low value of Seebeck coefficient and electrical conductivity. Highest thermoelectric power factor was obtained in BaTiO3 at 1200 K. Elastic constant were used to explain the mechanical properties such as anisotropic, brittle characteristics, stiffness and many others.

The structural, electronic and optical properties of pure Cadmium sulfide (CdS) and its alloy Cdx-1AxS(A = Co, Fe and Ni) compounds were investigated using first principle based on density functional theory. Electronic band structure and optical parameters calculations were performed using two different methods; generalized gradient approximation in Perdew-Burke-Ernzerhof (PBE) as well as modified Becke-Johnson (mBJ) for the exchange-correlation potential. Lattice constant, volume and bulk modulus were evaluated for structural properties. The results of band structure, effective mass, density of states and magnetic moment were determined for electronic properties. Optical parameters including absorption coefficient, refractive index, optical conductivity and optical reflectivity have been computed from the dielectric function at energy range of 0 to 15 eV using the Kramers-Kronig transformations. Our results reveal that the present of dopant in pure CdS enhanced the absorption capacity at low energy regions with the absorption coefficient of Cd0.75Fe0.25 > Cd0.75Co0.25S > Cd0.75Ni0.25S > Pure CdS for the GGA-PBE method and Cd0.75Fe0.25 > Cd0.75Ni0.25S > Cd0.75Co0.25S > Pure CdS for the mBJ method. The ability of Cd0.75Fe0.25 and Cd0.75Ni0.25S to absorb at extensive range of electromagnetic radiation makes them potential materials for application in nano-optoelectronic industry. All the results were compared with available theoretical calculations and the experimental data.

Dye-Sensitized Solar Cell (DSSC), as a unique non-conventional energy system, is rapidly gaining more attention from researchers. Efforts to fabricate photovoltaic devices with high conversion efficiencies at low cost with a simple fabrication process have prompted researchers to continuously work on different components of DSSC. This research focuses on the effect of precipitating agents, sodium hydroxide, and ammonium hydroxide on the fabrication of ZnO-based DSSCs. ZnO nanoparticles were prepared and characterized based on structural and microstructural analyses, UV-absorption and reflectance spectroscopy, and FTIR analysis, as one of the potential semiconductor photo-anodes for DSSCs. The uniformly prepared films using the doctor blade technique were soaked in Ruthenizer 535-bisTBA dye solutions for sensitization. The films were assembled and current-density characteristics measurements were taken using a solar simulator at 100 mW/cm2 and 25 °C. The effect of precipitating agents on the performance of the fabricated DSSC was studied. Photovoltaic performance evaluation of DSSCs using N719 dye as a sensitizer revealed that the open-circuit voltage (VOC) ranged between 0.535 and 0.719 V, and the short-circuit photocurrent density (JSC) was in the range of 3.621 to 5.875 mAcm−2. The highest conversion efficiency of 2.43 % was recorded for the synthesized ZnO semiconductor photo-anode using NaOH as the precipitating agent.

The emergence of dye sensitized solar cell (DSSC) as an alternative device for silicon based solar cell has gained a lot of attention from researchers due to its cost-effective, easy fabrication and environmentally friendliness. Photoanodes are semiconductor and as one of the four components of DSSC plays a major role for dye loading and electron conduction. A good photo anode should provide an efficient surface area in dye loading, nanostructure for high light harvesting opportunity, fast electron transport ability and good band gap architecture. Several nanostructures materials have been studied and employed as photoanode in DSSC. They include TiO2, ZnO, Nb2O5, SnO2, among others. The problem associated with photoanodes used in fabricating DSSC is high recombination rate of electrons that emanate from the number of grains. The dispersed nature of progress reports on developments of photoanodes calls for summary. Hence this review gives a general summary of the progress made in various materials used as photoanode in DSSC and the methods adopted in synthesizing them. In this present review, our attention is not only on synthesis and characterization of the materials alone but also on the effect of different factors influencing photovoltaic characteristics of photoanode for DSSC application.

Nano-sized particles of silver (Ag) whose diameter falls within 1-100 nm range possess an exceptional physico-chemical, biological and antimicrobial properties. As a result of their unique properties, silver nanoparticles (AgNPs) have been vigorously investigated. In the last decade, several trials have been made to heighten the green methods of formulating AgNPs to reduce the danger of the by-products from chemical methods. A clear understanding of AgNPs properties is absolutely necessary in order to make the best use of these nanoparticles in various fields, while their effect on man and environment is reduced to the least achievable. This review aims to discuss the green methods of preparing AgNPs and its numerous applications in the area of opto-electronics and environmental remediation. Many natural biomolecules in plants and microorganism were involved in formation, stabilization and bio-reduction of AgNPs. Over the years, several discoveries have reiterated that the catalytic and optical properties of AgNPs are dependent on the size, size-distribution and shape, which show variation by differing their synthetic approaches, stabilizers and reducing agents. In this review, silver nanoparticles have been reported to produce a desired result as a promising photocatalytic material and with a viable application in opto-electronic device. Thus silver nanoparticles are considered useful for having diverse range of applications for the benefits of man.

The photovoltaic (PV) system output performance is not independent as it varies over extended periods as well as it depends on the varying atmospheric conditions. In this work, the effect of ambient temperature and relative humidity on the efficiency performance of the polycrystalline PV system was investigated and analyzed in a tropical region. This was done by using a measurement system consists of sensors for measuring both electrical of the system and the atmospheric parameters concurrently at interval of time for a period of a year at the back of Pure and Applied Physics Department, Ladoke Akintola University of Technology Ogbomoso, Nigeria. From the measurements obtained, it was deduced that the performance efficiency of the system varied with the variation in the magnitude of the atmospheric parameters. The maximum daily value of efficiency obtained was 55% between the ambient temperature and relative humidity of 33oC to 34oC and 50% to 55% respectively. This can serve as a baseline to the PV designers and users for adequate installation of the system in the study area and other areas that have similar solar characteristics.Key words: Photovoltaic, polycrystalline, solar cell, semiconductor, efficiency.Corresponding Author

As a result of twin problems of environmental pollution and continuous depletion of fossil fuels, a search for renewable and clean energy sources is necessary. This paper discusses the simple extraction techniques without any further purification of natural dyes from some fruit peels and their performance in DSSCs. Natural dyes extracted from fruit peels of Carica papaya, Citrus lanatus, Persea americana and Solanum melongena were used as sensitizers to fabricate ZnO-based dye-sensitized solar cells (DSSCs). The extracts of the natural dyes were characterized and studied using UV-Vis absorption spectroscopy, Fourier transforms infra-red (FTIR) and Photoluminescence (PL) spectroscopy. The photo-anode semiconductor material was prepared and characterized. The photo-voltaic characteristics of the fabricated DSSCs were measured under simulated solar light (power of incident light 100 mWcm-2 from Air Mass 1.5G). These studies indicated the presence of pheophytin ‘a’ in most of the extracts studied as the main pigments with other accessory pigments. The solar to electric conversion efficiencies for the pheophytin ‘a’ dye based solar cells are estimated as 0.017%, 0.013%, 0.010% and 0.011% for Carica papaya, Citrus lanatus, Persea americana and Solanum melongena, respectively. The dye extracts from Carica papaya exhibits higher photo-sensitized performance compared to the other extracts and this is due to the better charge transfer between the dyes of Carica papaya and ZnO photo-anode surface. Conversion of visible light into electricity was accomplished with natural dyes and ZnO-based DSSCs, resulting in excellent photo-electric properties compared to those in literature.

The knowledge and estimation of solar radiation are very important in utilization of solar energy at any particular location especially when there is lack of measuring.In this study, meteorological parameters were used to model global solar radiation for solar energy applications.This was done by developing a number of regression equations for predicting daily/monthly solar radiation in Ogbomoso.Ogbomoso is a tropical area in the western part of Nigeria with Latitude 8.3" and logitude 4.2'E.The regression equations were obtained by modifying an existing Angstron equation as the base.The performance of these correlated models as global solar radiation estimators were evaluated by comparing the predicted values with the measured ones.Different statistical analyses were employed to examine the mathematical models.From the results, it is deduced that all the fits were consistent with the measurement but the quadratic model appeared to be the best of all the models which produced R2 of 95.3% the power model had the least R2 of 83.7%.The quadratic model proposed was compared with some existing quadratic models for some tropical stations and it was observed that the proposed quadratic models for some tropical stations and it was observed that the proposed quadratic equation KTP = 0.461+0.039T-0.001T2 is well correlated for the study area.Hence, the proposed model can be employed in designing of any solar energy applications in the study area and recommend for any other areas having similar characteristics with the area of study.