Technology has always been inspired by nature. This is one of the reasons why new technologies continually seek environmentally friendly composite materials. In recent years, there has been a growing interest in developing green bio-composites for industrial wastewater treatment.

In this work, we prepared a type of green, low-cost hybrid composite material comprising volcanic rock (VR), a natural Algerian siliceous volcanic filler from Ain-Temouchent, and the biopolymer alginate (Alg).

The Alginate/Volcanic Rock (Alg/VR) beads were prepared using a simple mixing method in the form of beads, produced with a syringe pump and a cross-linking agent. Detailed characterization of the beads and their initial reagents was carried out using X-Ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), and Thermogravimetric Analysis (TGA). The results confirmed the incorporation of the biopolymer into the natural volcanic rock matrix, with clear evidence of interaction between alginate and volcanic rock.

Furthermore, the beads were tested as effective and alternative adsorbents for the removal of the cationic dye Malachite Green (MG) using a Flow-through cell apparatus. The influence of different experimental parameters, such as pH, contact time, adsorbent dose, and initial dye concentration, was investigated. The adsorption results showed that the highest removal efficiency of 95% was achieved at pH 6, with a contact time of 60 minutes, using 0.8 g/L of the composite for a 25 ppm dye solution.

These findings highlight the significant potential of Alg/VR beads as a low-cost, sustainable, and efficient adsorbent for industrial wastewater treatment. By combining locally sourced natural materials with biopolymers, this work not only contributes to green chemistry and sustainable environmental management but also offers a practical solution for addressing global water pollution challenges. This innovative approach aligns with the increasing demand for eco-friendly technologies and reinforces the importance of developing scalable, cost-effective solutions for industrial applications.

Introduction

This study develops eco-friendly catalysts using kojic acid, halloysite nanotubes, and alginic acid to create sustainable materials for CO₂ reduction and fixation.

Methods

HNTs functionalized with KA (HNT-KAs) wwere synthesized by reacting HNTs with chloroKA (ClKA) in DMF at 80 °C overnight, using Et₃N as a base. The use of three ClKA ratios produced HNT-KA1, HNT-KA3, and HNT-KA6. FT-IR confirmed their functionalization, and TGA was used to assess their thermal stability. SEM-EDX and TEM characterized their morphological properties. CO₂ photoconversion experiments were conducted under simulated solar irradiation for 7 hours, using hydrogen as the reducing agent in the presence of copper ions. Copper, chelated by the KA moiety, was introduced via CuCl₂ and reduced into Cu(I) using ascorbic acid. AA functionalized with KA (AA-KA) was synthesized through nucleophilic substitution with ClKA in dry DMF at 40 °C. Both catalysts were tested for their CO₂ fixation into cyclic carbonates at 70 °C and 1 atm using TBAB as a co-catalyst. Styrene epoxide was used as the model substrate, and the catalysts' recyclability was evaluated based on their insolubility in organic solvents.

Results

HNT-KA6 showed the best performance among the tested ratios, achieving 31% CO₂ photoreduction into methane and 89% CO₂ conversion into cyclic carbonates, surpassing the same values for HNT-KA1 and HNT-KA3. Adding Cu(I) increased the CO₂ photoreduction efficiency threefold and the methane selectivity fourfold while maintaining the stability over four cycles. HNT-KA6 also demonstrated strong CO₂ fixation activity without copper, as KA facilitated CO₂ capture and opening of the epoxide ring. AA-KA was highly efficient, achieving optimal yields with a continuous CO₂ flow at 70 °C for 10 hours. Both catalysts worked effectively under mild, solvent-free conditions, delivering higher yields than those previously reported.

Conclusions

The HNT-KA6 and AA-KA catalysts demonstrate high potential for sustainable CO₂ conversion. Their efficiency under mild, solvent-free conditions and their excellent recyclability make them ideal for green chemistry, supporting eco-friendly solutions for climate change mitigation.

Complexation helps to increase the solubility as well as improving other qualities of drug substances. To study this process and subsequent preparation of compounds, we chose γ-cyclodextrin and nimesulide, a widely used drug for the treatment of acute and chronic pain.

To obtain the inclusion complexes, we used a combination of methods: co-evaporation and coprecipitation. Varying some parameters of complexation (the pH of the reaction mixture (pH = 3; pH = 7), and the presence and volume of additional solvent (acetone)), several samples of putative complexes were obtained as a result of the experiment. Qualitative analysis was carried out by FTIR spectroscopy on a Fourier spectrometer (‘FMS 1201’, Russia). The obtained IR spectra suggest that some functional groups of nimesulide (S=O, R-NO2) interacting with functional groups of γ-CD lead to a shift in the corresponding absorption bands. The formation of the complex was further confirmed by differential scanning calorimetry. The change in the enthalpy of phase transition with respect to the pure substance indirectly testifies to the formation of the complex compound. The quantitative composition of inclusion complexes was studied using a calibration plot method on a Shimadsu UV-1800 UV spectrometer. Quantitative analysis showed that the most complete incorporation of nimesulide into the cavity of γ-CD is achieved with the addition of an additional solvent (acetone) and the observance of an acidic environment in the reaction mixture. A change in other parameters (temperature or time of mixing the reaction mixture) did not have a noticeable effect on the process. the toxicological activity of the obtained compounds was not studied. Based on the confirmed safety of nimesulide and γ-CD, we assume that the complexes are also non-toxic.

Thus, knowing the factors that have a predominant influence on the process of complexation, it is possible to obtain inclusion complexes of cyclodextrins with various drugs, creating new modified forms.

Arsenic contamination in water poses a significant health risk, making effective removal methods essential. Low-cost biosorbents and easy magnetic separation are desirable for this purpose. While various magnetic adsorbents have been developed using the coprecipitation method, challenges remain due to arsenic's toxicity and WHO limitations. This study introduces nanomagnetite-coated biochar derived from pecan nutshells as an efficient arsenic adsorbent, utilizing a solvothermal method. This controlled synthesis enables the precise growth of magnetite crystals on biochar, resulting in uniform particle size and morphology. The process occurs in Teflon-lined stainless-steel autoclaves at 200°C, with reaction times ranging from 6 to 12 hours. Iron chloride acts as the iron ion precursor, and ethylene glycol serves as the solvothermal medium. Pecan nutshell biochar particles, sized 0.10-0.18 mm and 0.18-0.38 mm, are produced via pyrolysis at 700°C for 1 h under nitrogen. Following solvothermal treatment, the resulting particles are magnetically separated from the solution. Characterization via XRD, SEM, TEM, and FTIR confirms the formation of homogeneously magnetite-coated biochar particles. This method yields homogeneous nucleation and the growth of nanometric magnetite crystals on the surface of biochar particles, leading to a narrow size distribution and consistent morphology without other crystalline phases, enabling high arsenic adsorption rates (97.30-98.76%) from water. Notably, biochar with varied particle sizes synthesized at a short reaction time (200°C, 6 h) demonstrates the highest arsenic removal efficiency (98.76%) and adsorption capacity (7.974 mg/g), comparable to magnetite nanoparticles. The development of nanomagnetite-coated biochar derived from pecan nutshells showcases significant innovative potential in addressing arsenic contamination. This is due to several factors: the sustainable use of biochar from pecan nutshells, nanomagnetite coating for efficient arsenic removal, the controlled synthesis process, high adsorption capacity, low-cost biosorbents, ease of magnetic separation, and versatility for removing other contaminants.

AgCaCl₃, an inorganic halide perovskite material, is recognized for its high stability and environmental compatibility, making it a promising candidate for significant applications in optoelectronics and lens manufacturing. This study focused on investigating the electronic properties of AgCaCl₃, including its density of states and band structure. The results revealed that AgCaCl₃ consistently exhibits an indirect band gap of around 1.5 eV across the pressure range examined. Furthermore, its dielectric function, absorption coefficient, optical conductivity, reflectivity, and refractive index indicated that AgCaCl₃ maintains its optical properties under the conditions studied. The mechanical properties were also analyzed, with calculations of elastic constants (C₁₁, C₁₂, and C₁₄) providing insights into the material's dynamic stability. Parameters such as the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and anisotropy factor suggest that the material is ductile. Additionally, thermal properties, including the Debye temperature, isobaric and isochoric heat capacities, thermal expansion coefficient, Gibbs free energy, and entropy, were thoroughly examined.

Methods
This study utilized DFT calculations, implemented in the Wien2K code, to explore the mechanical and thermal properties of AgCaCl₃ under varying pressure conditions. Its electronic and optical properties were optimized using the PBE-GGA functional. Its mechanical and thermodynamic properties were calculated using the ElaStic and Gibbs2 codes.

Results and conclusions

This study investigates the physical, mechanical, and thermal properties of AgCaCl3 under different pressures. The results show a decrease in its volume and lattice constants as pressure increases, while the material maintains its semiconductor properties and stable optical behavior. These computational findings highlight AgCaCl3's potential for use in deep-sea devices and lenses. Its elastic properties were found to increase linearly with the applied pressure, and its thermal characteristics, modeled using the quasi-Debye approach, provided detailed insights into the material’s response. These outcomes form a solid foundation for future experimental work, supporting the development and application of AgCaCl3 in optoelectronic devices.

This presentation will focus on the evolution and recent developments of a new class of photoluminescent materials referred to as Carbon dots or C-dots, primarily comprising C, H, O, and N. Typically, C-dots have spherical shape with sizes lower than 20 nm, and can be synthesized at a large scale following the simple pyrolysis treatment of suitable carbon-rich precursors, including crude biomass, renewable resources, polymers, and carbon fibres (1,2). Depending on the preparation method and the nature of the starting materials, the graphitization degree, elemental composition and the morphology of C-dots can vary considerably, while post-synthesis treatments (such as chemical and electrochemical reactions, passivation strategies and physio-absorption) can modify their surface characteristics, thereby enhancing their solubility, biocompatibility, toxicity and optical properties (3).

In principle, C-dots demonstrate excitation wavelength-dependent emission with high quantum yields with the strongest emissions falling within the blue/green area, although red-emissive systems have also been reported (4). Moreover, the significant role of the organic fluorophores generated during the pyrolytic synthesis of C-dots has been demonstrated (5). Interest lies in the optical properties of C-dot-based aqueous dispersions, solid-state materials, polymer nanocomposites and nanopowders. This presentation will provide an overview of the structure--property relationships of C-dots with emphasis on emerging applications such as bioimaging, phototherapy, controlled drug release, molecular sensing, antimicrobial treatments, fertilisers, catalysis, energy conversion, nanoforensics, water treatment, environmental decontamination and anti-counterfeiting (6,7).

References

1. Stachowska, J.D.; Murphy, A.; Fernandes, D.; Gibbons, E.N.; Krysmann, M.J.; Kelarakis, A.; Burgaz, E.; Moore, J.; Yeates, S.G. Sci. Rep. 2021, 11, 10554
2. Krysmann, M.J.; Kelarakis, A.; Giannelis, E.P. Green Chem. 2012, 14, 3141
3.Kelarakis, A. Curr. Opin. Colloid Interface Sci. 2015, 20, 354
4.Gavalas, S.; Kelarakis, A. Nanomaterials 2021, 11, 2089
5. Krysmann, M.J.; Kelarakis, A.; Dallas, P.; Giannelis, E.P. J. Am. Chem. Soc. 2011, 134, 747
6. Fernandes, D.; Krysmann, M.J.; Kelarakis, A. Chem. Commun. 2015, 51, 4902
7.Verhagen, A.; Kelarakis, A. Nanomaterials 2020, 10, 1535

The development of physical methods of high-energy impact on the material makes obtaining a substance in a nano-dispersed state possible. The difference between nanoparticles obtained by the electrospark method, when condensation of the metal vapor phase occurs in a dispersion medium (water), the temperature of which does not exceed 30-40 degrees C, is a relatively narrow distribution of particles of the dispersed phase (20 - 100 nm). The field of application of such substances is not limited to agrobiological purposes. The authors investigated the electrospark metal granular dispersion method in an aqueous medium. The particles obtained by the above method have a size of 20-100 nm and several competitive advantages compared with similar methods of synthesis of metal nanoparticles. The level of defects in the crystal structure of nanoparticles after electro spark treatment is significantly higher than the values achieved by known methods of hardening metals and alloys. The high level of dislocation density in nanoparticles determines their high energy saturation. The study of the fine structure showed that the level of dislocation density in nanoparticles is close to the limit values of 1014 cm-2 as a result of the joint action of shock waves that arise in the process of pulse expansion of electric spark channels under the influence of pressure of several hundred atmospheres, high cooling rate of more than 103-104 °C/s. Analysis of the internal structure of the obtained nanoparticles shows that their composition is heterogeneous. The particle is a metallic nucleus on which an oxide film is formed. In addition, iron particles can have a complex phase composition, namely, contain (consist of) alpha-iron and gamma-iron, which further expands the physical and technological aspects of using particles with a sharply non-equilibrium structural and phase composition.

Over the last decade, fully inorganic lead halide perovskite nanocrystals (NCs) have received a lot of attention as active materials for photonic and optoelectronic devices. Despite their high sensitivity to ambient conditions typically inducing irreversible degradation mechanisms, some experiments have evidenced reversible environmental effects, clearing the way for their application as active materials for resistive and optical sensors. In particular, the sensitivity of CsPbBr₃ NC thin films to ambient air was demonstrated, noticeable as reversible modulation of the PL and ASE intensities, which is a sign of physical perovskite–air interactions, ruling out degradation effects. The air's humidity determines the solvation of the surface and the hydrophilic ligand's head group, resulting in the formation of surface trap states that modulate the emitted PL intensity; in a vacuum, water molecules can be desorbed, restoring pristine conditions. Moreover, the stimulated emission demonstrated a higher sensitivity (up to 6.5 times higher) to ambient air compared to that of the spontaneous emission, opening the way for the realization of ASE-based optical gas sensors with perovskites.

Since the PL and stability properties of the NCs strongly depend on their surface chemistry and, in particular, on the surfactant molecules used to passivate the surface defects, we performed a systematic investigation of the effects of the NC capping ligands on the ASE and sensing properties of CsPbBr₃ thin films. In particular, our experiments were performed on four different samples, representatives of three generations of capping ligands: oleic acid and oleylamine (OAc/OAm) as the first, didodecyldimethylammonium-bromide (DDAB) as the second, and 3-(N,N-dimethyloctadecylammonio)propanesulfonate (ASC18) and lecithin as the third. The lowest ASE threshold was reported for the lecithin-capped NC sample, together with the strongest sensitivity to air. On the other hand, the OA-capped sample, which showed one of the highest ASE thresholds and the lowest sensitivity to air, was demonstrated to be highly stable under strong laser irradiation.

Wood is a highly sustainable material for building construction, yet its susceptibility to fire hazards limits its structural applications. Nitrogen-phosphorus (NP)-based compounds are the most preferred fire-retardant (FR) additives for timber applications. But their use in wood also results in some negative effects, such as the loss of mechanical strength in wood. This study explores the synergistic effects of Nano-Silica (NS) and NP-based compounds on enhancing the fire retardancy and mechanical properties of Hevea brasiliensis. A combination of ammonium polyphosphate (APP) and dicyandiamide (DCD) has been used in this study as an NP-based entity. Wood samples were treated by the full cell impregnation process with the following compositions: a) NS only at 1.5% (w/w) concentration: NS_1.5; b) NP-based combination, APP (17%, w/w) and DCD (3%, w/w): APP₁₇/DCD₃; and c) combination of NS_1.5 and APP₁₇/DCD₃: NS_1.5/APP₁₇/DCD₃. During the rate of burning test, the control and NS_1.5-treated samples showed very poor fire resistance, reaching only 40% mass loss, almost within a minute, while APP₁₇/DCD₃- and NS_1.5/APP₁₇/DCD₃-treated samples reached the same amount of weight loss in 2.5 and 3 minutes, respectively. During the three-point bending test, the modulus of elasticity (MOE) showed 29% and the modulus of rupture (MOR) showed 43% deterioration in APP₁₇/DCD₃-treated samples as compared to the control samples. But the combined NS_1.5/APP₁₇/DCD₃ treatment recovered the deterioration in MOE and MOR values by making it almost equivalent to the control samples. Thus, the results of the experiments in this study confirmed the excellent synergy of NS and NP-based compounds in H. brasiliensis wood, not only enhancing fire resistance but also addressing the issue of mechanical deterioration in wood due to the NP-based FR treatment.

Phosphate coatings obtained from solutions based on the drug containing Mn(H₂PO₄)₂∙2H₂O (proportion of phosphoric acid, in terms of P₂O₅ 46-52 % ; mass fraction of manganese not less than 14 %), used to protect steel products from corrosion. Phosphating solutions are widely used to produce protective films at low temperatures. To obtain colored coatings, it is proposed to introduce the dyes procyon olive green and methylene blue in the amount of 8 g/L into phosphating solutions. Colored phosphate films unevenly cover the surface of steel samples. The protective and physical and mechanical properties (thickness, heat resistance, wear resistance, breakdown voltage value) of colored phosphate coatings obtained on steel by the cold method are studied. The protective properties of phosphate coatings strongly depend on their thickness and the nature of the crystal structure, since the thickness and structure determine the porosity of the coatings, and, consequently, the freedom of access of the aggressive medium to the metal surface. It was found that phosphate coatings can withstand short-term heating up to 100 °C, after which their protective ability is greatly reduced. Colored phosphate films produced on steel by the cold method have low values of the coefficient of friction, but this disadvantage can be eliminated by impregnation with lubricants. The breakdown voltage of colored phosphate coatings is about 200 V. Its electrical insulation properties can be improved by impregnation with oil and bakelite lacquers.