Survey Summary on Salts Hydrates and Composites Used in Thermochemical Sorption Heat Storage: A Review

International audienceTo improve the proficiency of energy systems in addition to increasing the usage of renewable energies, thermal energy storage (TES) is a strategic path. The present literature review reports an overview of the recent advancements in the utilization of salt hydrates (single or binary mixtures) and composites as sorbents for sorption heat storage. Starting by introducing various heat storage systems, the operating concept of the adsorption TES was clarified and contrasted to other technologies. Consequently, a deep examination and crucial problems related to the different types of salt hydrates and adsorbents were performed. Recent advances in the composite materials used in sorption heat storage were also reviewed and compared. A deep discussion related to safety, price, availability, and hydrothermal stability issues is reported. Salt hydrates display high theoretical energy densities, which are promising materials in TES. However, they show a number of drawbacks for use in the basic state including low temperature overhydration and deliquescence (e.g., MgCl2), high temperature degradation, sluggish kinetics leading to a low temperature rise (e.g., MgSO4), corrosiveness and toxicity (e.g., Na2S), and low mass transport due to the material macrostructure. The biggest advantage of adsorption materials is that they are more hydrothermally stable. However, since adsorption is the most common sorption phenomenon, such materials have a lower energy content. Furthermore, when compared to salt hydrates, they have higher prices per mass, which reduces their appeal even further when combined with lower energy densities. Economies of scale and the optimization of manufacturing processes may help cut costs. Among the zeolites, Zeolite 13X is among the most promising. Temperature lifts of 35–45 °C were reached in lab-scale reactors and micro-scale experiments under the device operating settings. Although the key disadvantage is an excessively high desorption temperature, which is problematic to attain using heat sources, for instance, solar thermal collectors. To increase the energy densities and enhance the stability of adsorbents, composite materials have been examined to ameliorate the stability and to achieve suitable energy densities. Based on the reviewed materials, MgSO4 has been identified as the most promising salt; it presents a higher energy density compared to other salts and can be impregnated in a porous matrix to prepare composites in order to overcome the drawbacks connected to its use as pure salt. However, due to pore volume reduction, potential deliquescence and salt leakage from the composite as well as degradation, issues with heat and mass transport can still exist. In addition, to increase the kinetics, stability, and energy density, the use of binary salt deposited in a porous matrix is suitable. Nevertheless, this solution should take into account the deliquescence, safety, and cost of the selected salts. Therefore, binary systems can be the solution to design innovative materials with predetermined sorption properties adapted to particular sorption heat storage cycles. Finally, working condition, desorption temperature, material costs, lifetime, and reparation, among others, are the essential point for commercial competitiveness. High material costs and desorption temperatures, combined with lower energy densities under normal device operating conditions, decrease their market attractiveness. As a result, the introduction of performance metrics within the scientific community and the use of economic features on a material scale are suggested

CO2 Electroreduction over Metallic Oxide, Carbon-Based, and Molecular Catalysts: A Mini-Review of the Current Advances

International audienceElectrochemical CO2 reduction reaction (CO2RR) is one of the most challenging targets of current energy research. Multi-electron reduction with proton-coupled reactions is more thermodynamically favorable, leading to diverse product distribution. This requires the design of stable electroactive materials having selective product generation and low overpotentials. In this review, we have explored different CO2RR electrocatalysts in the gas phase and H-cell configurations. Five groups of electrocatalysts ranging from metals and metal oxide, single atom, carbon-based, porphyrins, covalent, metal–organic frameworks, and phthalocyanines-based electrocatalysts have been reviewed. Finally, conclusions and prospects have been elaborated

NiO/AC Active Electrode for the Electrosorption of Rhodamine B: Structural Characterizations and Kinetic Study

In this work, the aim was to enhance the performance of activated carbon (AC) as an electroadsorbent by incorporating NiO particles, thereby increasing its electrochemical capacity and its ability to adsorb Rhodamine B (RhB) dye. The prepared NiO/AC material was characterized using X-ray diffraction, scanning electron microscopy, BET surface area analysis, and infrared spectroscopy. The study involved the preparation of AC from almond shell biomass and the subsequent formation of a composite structure with NiO. The objective was to investigate the electrochemical adsorption capacity of the NiO/AC composite for RhB dye removal from simulated wastewaters. The experimental results demonstrated that the removal efficiency of RhB dye increased with an increase in the applied cell voltage. At a voltage of 1.4 V, a remarkable 100% removal efficiency was achieved. The electroadsorption process was well described by fitting the experimental data to the Freundlich isotherm model. The maximum adsorption capacities for RhB dye at concentrations of 7, 8, and 9 ppm were determined to be 149, 150, and 168 mg/g, respectively. Based on the obtained results, an electroadsorption mechanism was proposed to explain the observed behavior of the NiO/AC composite in adsorbing RhB dye. Overall, this study highlights the potential of the NiO/AC composite as an effective electroadsorbent for the removal of Rhodamine B dye from wastewater. The improved electrochemical capacity, coupled with the high adsorption capacity of the composite, makes it a promising material for wastewater treatment applications

Porous carbon materials derived from olive kernels: application in adsorption of organic pollutants

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Removal of reactive red-198 dye using chitosan as an adsorbent: optimization by Central composite design coupled with response surface methodology

International audienceShrimp shells were used to prepare chitosan as an adsorbent for reactive red 198 dye removal. The adsorption of reactive red 198 (RR-198) on chitosan has found to be dependent on some parameters such as pH, concentration, and temperature. These parameters were studied in the batch system to study the optimum adsorption conditions. The experimental result follows Langmuir isotherm model and the adsorption ability was found to be 357.1 mg/g. The pseudo-second-order equation was the best applicable model to describe the adsorption. Finally, the effect of different parameters affecting the adsorption was studied using central composite design matrix coupled with response surface methodology. Overall, this work shows that chitosan material based shrimp shells have countless potential to be used for dyes removal in wastewater treatment plants. Further fine-tuning of this material may open the field of their application

Well-designed WO₃/Activated carbon composite for Rhodamine B Removal: Synthesis, characterization, and modeling using response surface methodology

<p>This study focuses on the preparation of WO₃ oxide nanoparticle/Activated carbon composite (WO₃/AC) for Rhodamine B (RhB) adsorption. The prepared samples were characterized using X-Ray Energy Dispersive Spectroscopy (EDS) and Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller surface area (BET), Raman Spectroscopy and Thermogravimetric analyses (ATG-ATD). Adsorption experiments of RhB onto WO₃/AC were carried out in a batch reactor and different operational parameters were investigated. The RhB adsorption process was well fitted by pseudo-second-order kinetic and Langmuir isotherm models (1666.67mg.g⁻¹). Moreover, the values of thermodynamic parameters indicate the spontaneous, endothermic and physisorption adsorption nature. Finally, adsorption mechanism was proposed on the basis Raman analyses before and after adsorption.</p

Synthesis of nanosized TiO2 powder by sol gel method at low temperature

International audienceNanotechnology is all about making products from very small constituents, components or subsystems to gain greatly enhanced material properties and functionality. Nanocrystalline anatase TiO2 was prepared by a facile sol–gel route at a temperature of 50°C under mild conditions. Titanium tetraisopropoxide (TTIP) was used as a titanium precursor, and 2-propanol was used as a solvent. XRD, TEM, SEM, FT-IR and BET were applied to characterize the crystal phase. The Crystalline size of TiO2 powder has been obtained with diameter < 30 nm for anatase at 500°C using an acid

MXenes as Electrocatalysts for Energy Conversion Applications: Advances and Prospects

International audienceHydrogen as a potential future energy source provides a number of benefits in terms of sustainability, high energy density, and zero emissions. The production of hydrogen via water splitting is regarded as the cleanest and sustainable process. In contrast, fossil fuel combustion causes significant environmental problems through the production and release of secondary gases such as NO x , SO 2 , and CO 2 . It is vital to focus on reducing these harmful gases. CO 2 , a major pollutant produced by the combustion of fossil fuels and various human activities, plays a central role in the greenhouse effect and contributes to global warming. It is therefore imperative to actively eliminate and mitigate CO 2 levels to preserve the global environment. MXenes and MXene‐based catalysts exhibit both outstanding hydrogen evolution reaction (HER) performance and CO 2 reduction. In this review, recent progress is systematically examined and discussed in the preparation and utilization of MXenes as catalysts for HER and carbon dioxide reduction reaction (CO 2 RR). The discussion begins with a concise overview of the fabrication and characteristics of MXenes, followed by a comprehensive exploration of their efficacy as catalysts for HER and CO 2 RR

Heat storage: Hydration investigation of MgSO4/active carbon composites, from material development to domestic applications scenarios

International audienceThe scarcity of durable and low-cost sorbent materials remains a significant technological barrier to long-term heat storage. In the present work, composite materials based on activated carbon supports and magnesium sulfate hydrates (labelled MgSO4/AC) were developed in order to increase the energy density and improve mass and heat transport phenomena. The results of composite characterization revealed uniform dispersion of magnesium sulfate in composites produced via incipient wetness impregnation. The hydration enthalpy increased as the MgSO4 content on AC increased, reaching a plateau for MgSO4 content of more than 30%wt (30-MgSO4/AC and 40-MgSO4/AC samples). The hydration experiment performed on the 30-MgSO4/AC sample at RH = 60% verified the relation between the salt hydration level and the hydration enthalpy. Higher water partial pressure enhanced water molecule transport and improved salt hydration. The hydration enthalpy of 30-MgSO4/AC showed an increase from 859 J/gdry material at RH = 30% to 1324 J/gdry material at RH = 60%. After 8 cycles of hydration/dehydration, the 30-MgSO4/AC sample was practically stable. Furthermore, the 30-MgSO4/AC) composite was modeled in two distinct scenarios for house heating and sanitary hot water generation. Finally, the experimentally obtained calorimetric data were used to implement a numerical model. Two different scenarios were considered, the first for heating a house and the second for producing hot sanitary water. Both scenarios show the possibility of using the MgSO4/AC composite in a multifunction thermochemical heat storage system

Adsorption kinetics and surface modeling of aqueous methylene blue onto activated carbonaceous wood sawdust

<p>In this work, Sawdust was used to develop a new low-cost adsorbent and study its application to remove methylene blue dye from aqueous solution. Sawdust was calcined under air atmosphere at three different temperatures (300°C, 400°C, and 500°C) using phosphoric acid (H₃PO₄) as an activating agent. The structure, morphology, surface functions and the chemical composition of adsorbent were characterized by Fourier Transform Infrared spectra (FTIR), X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), specific surface area (BET) and Boehm method. Different operational parameters such as pH, adsorbent loading, contact time and were investigated to evaluate experimental data. The adsorption of MB on SD-300, SD-400, and SD-500 show that the pseudo-second-order and Langmuir models fitted better the experimental results of MB adsorption onto all adsorbents. The maximum capacities based on the Langmuir model were 416.7 mg.g⁻¹ for SD-300, 526.3 mg.g⁻¹ for SD-400, and 819.7 mg.g⁻¹ for SD-500. The positive values of ΔG, ΔH, and ΔS implied that the adsorption process was non-spontaneous and endothermic nature. Finally, Regeneration of the SD-500 was investigated and optimization was performed using CCD combined with RSM.</p