Guanidine Carbonate Research Articles

Phosphorus-Nitrogen Interaction in Fire Retardants and Its Impact on the Chemistry of Treated Wood.

This work focuses on the changes in the chemical composition of wood caused by impregnation with fire retardants such as guanidine carbonate (GC), urea (U), diammonium phosphate (DAP) and their mixtures. The treated wood was tested using the oxygen index (LOI), Py-GC/MS analysis and FTIR Spectroscopy. The wood was vacuum treated at a pressure of 0.8 MPa for 20 min and then subjected to thermal degradation using the LOI. This way, degraded and nondegraded layers were obtained and ground (0.2 mm). All treatment variants achieved the class of non-flammable materials based on LOI tests; the exception was the 5% urea solution, defined as a flame-retardant material. Using the analytical methods, it was found that cellulose and hemicelluloses undergo the fastest thermal degradation. This study found that the variant protected with a 5% mixture of GC and DAP before and after the degradation process had the best fire-retardant properties regarding cellulose content in the wood. The highest content of anhydrosugars characterised the same variants, the amount of which indicates a slowdown in the degradation process and, consequently, a reduction in the release of levoglucosan during combustion, suggesting potential applications in fire safety.

Mining for antifungal agents to inhibit biofilm formation of Candida albicans: A study on green synthesis, antibiofilm, cytotoxicity, and in silico ADME analysis of 2-amino-4H-pyran-3-carbonitrile derivatives

Candida albicans (C. albicans) biofilm infections are quite difficult to manage due to their resistance against conventional antifungal drugs. To address this issue, there is a desperate need for new therapeutic drugs. In the present study, a green and efficient protocol has been developed for the synthesis of 2-amino-4H-pyran-3-carbonitrile scaffolds 4a-i, 6a-j, and 8a-g by Knoevenagel-Michael-cyclocondensation reaction between aldehydes, malononitrile, and diverse enolizable C-H activated acidic compounds using guanidinium carbonate as a catalyst either under grinding conditions or by stirring at room temperature. This protocol is operationally simple, rapid, inexpensive, has easy workup and column-free purification. A further investigation of the synthesized compounds was conducted to examine their antifungal potential and their ability to inhibit the growth and development of biofilm-forming yeasts like fungus C. albicans. According to our findings, 4b, 4d, 4e, 6e, 6f, 6g, 6i, 8c, 8d, and 8g were found to be active and potential inhibitors for biofilm infection causing C. albicans. The inhibition of biofilm by active compounds were observed using field emission scanning electron microscopy (FESEM). Biofilm inhibiting compounds were also tested for in vitro toxicity by using 3T3-L1 cell line, and 4b, 6e, 6f, 6g, 6i, 8c, and 8d were found to be biocompatible. Furthermore, the in silico ADME descriptors revealed drug-like properties with no violation of Lipinski's rule of five. Hence, the result suggested that synthesized derivatives could serve as a useful aid in the development of novel antifungal compounds for the treatment of fungal infections and virulence in C. albicans.

Effective direct steam regeneration of bis-iminoguanidine solid sorbent used for carbon dioxide capture

A cost-effective, energy-efficient sorbent regeneration process for phase-changing guanidines used for CO2 capture was developed based on direct-steam stripping. This approach enhances the regeneration rate, simplifies the overall CO2 capture process, and reduces the energy cost compared to conventional conductive thermal regeneration. A direct-steam sorbent regeneration reactor was developed, demonstrating that aqueous bis(iminoguanidines) (BIG) sorbents, e.g., methylglyoxal-bis(iminoguanidine) (MGBIG) and glyoxal-bis(iminoguanidine) (GBIG), could be efficiently regenerated with up to ∼ 99 % CO2 recovery through direct-steam stripping. Using low-temperature steam at 100 °C, a 4.5 times faster regeneration rate for GBIG carbonate sorbent (e.g., 30 min for 10 g) was demonstrated compared to conductive-heating (e.g., 135 min for 10 g) at 130 °C. Additionally, fully regenerated MGBIG converts into an aqueous MGBIG solution when the steam condenses onto the sorbent surface. Condensed steam with the guanidine can be easily recycled as an aqueous solution into the gas–liquid contactor to achieve a continuous-flow CO2-capture process. Molecular dynamics simulation was employed to provide a better understanding of the process. Higher heat transfer rates from steam to guanidine carbonate, compared to air heating, were attributed to the vibration resonance of water molecules within MGBIG with that of vapor molecules and the effective transfer of kinetic energy from vapor to solid. Technoeconomic analysis demonstrated that direct-steam stripping significantly decreases the CO2 capture cost by 50 % compared to traditional conductive heating methods. Enhanced mass transfer facilitated by low-temperature steam and subsequent condensation effectively heats up the H2O-containing BIG-carbonate crystals, facilitating the desorption of CO2 from the solid crystals, thereby leading to fast, effective, and energy-efficient sorbent regeneration.

Guanidine carbonate modified TiO2/Perovskite interface for efficient and stable planar perovskite solar cells

The rational design and modification of the buried interface are essential and challenging for high-performance perovskite solar cells (PSCs). TiO2 is a simple and readily available electron transport layer material, but its surface defects and poor interfacial contact with perovskite layers hinder its widespread application. Here, we propose an effective TiO2/perovskite interface modification strategy by introducing simple guanidine carbonate (GuaCO3) onto the surface of TiO2. Guanidine carbonate can improve the interfacial contact between TiO2 and perovskite, reduce non-radiative recombination, and enhance carrier extraction. Moreover, the PbI2 film grown on the TiO2/GuaCO3 substrate tended to become porous during the preparation of perovskite films by the traditional two-step method, which facilitated the complete reaction of organic ammonium salts with PbI2 and promoted the growth of high-quality perovskite films. The experimental results indicate that GuaCO3 can passivate the interfacial defects of TiO2/perovskite, as well as reduce the accumulation of interfacial charges. The device modified with GuaCO3 achieved a power conversion efficiency (PCE) of 23.39 %, which is significantly higher than that of the control device (21.73 %). After storage in an ambient environment at room temperature for 600 h, the unencapsulated device modified with GuaCO3 retained 78 % of its initial efficiency, while the control device retained only 57 % of its initial efficiency. These results indicate that interfacial modification with GuaCO3 is an effective strategy for improving the performance of PSCs.

Nanostructured Niobium and Titanium Carbonitrides as Electrocatalyst Supports.

Nanostructured niobium-titanium carbonitrides, (Nb,Ti)C1-xNx, with the cubic-rock salt structure are prepared without the use of reactive gases via thermal treatment (700-1200 °C) under nitrogen of mixtures of guanidine carbonate and ammonium niobate (V) oxalate hydrate, with addition of ammonium titanyl oxalate monohydrate as a titanium source. The bulk structure and chemical composition of the materials are characterized using powder X-ray diffraction (XRD) and powder neutron diffraction, elemental homogeneity is studied using energy dispersive spectroscopy (EDS) mapping using transmission electron microscopy (TEM), and surface chemical analysis is examined using X-ray photoelectron spectroscopy (XPS). Nanoscale crystallites of between 10 and 50 nm are observed by TEM, where EDS reveals the homogeneity of metal distribution for the mixed-metal materials. Titanium carbonitrides are found to be air sensitive, reacting with air under ambient conditions, while titanium-niobium carbonitrides are found to degrade in aqueous sulfuric acid. The niobium carbonitrides, however, show some stability toward acidic solutions. Materials are produced with composition NbC1-xNx with x between 0.35 and 0.45, and more carbon-rich materials (x ≈ 0.35) are found as the synthesis temperature is increased, as proven by Rietveld refinement of crystal structure against powder neutron diffraction data. Despite phase purity seen by diffraction and negligible bulk carbon content, XPS shows a complex surface chemistry for the NbC1-xNx materials, with evidence for Nb2O5-like oxide species in a carbon-rich environment. The NbC1-xNx prepared at 900 °C has a surface area around 50 m2 g-1, making it suitable as a catalyst support. Loading with iridium provides a material active for the oxygen evolution reaction in 0.1 M sulfuric acid, with minimal leaching of either Nb or Ir after 1000 cycles.

Atomic surface induced by novel green chemical mechanical polishing for aspheric thin-walled crucibles with large diameters

Aspheric thin-walled crucibles with large diameters are widely used for photovoltaics and semiconductor industries, while they have hard-brittle and aspheric characteristics. Nevertheless, these crucibles strictly require atomic surfaces and high material removal rate (MRR). This is a challenge for chemical mechanical polishing (CMP). To break this challenge, a novel green CMP was developed for fused silica, containing ceria, lanthana, hydrogen peroxide, diethylene triaminepentaacetic acid pentasodium, carboxymethyl cellulose sodium and guanidine carbonate. After CMP, surface roughness Ra of 0.115 is obtained at a scanning area of 5 × 5 μm2 measured by atomic force microscopy, and MRR is 563 nm/min. In such an atomic surface, the MRR is the highest compared with those published previously. Transmission electron microscopy confirms that the thickness of damaged layer after CMP is only 2.63 nm. A novel approach of robot floating polishing is proposed for aspheric crucibles with a diameter of 810 mm and a height of 580 mm. Using the developed CMP, surface roughness Sa of 0.178 nm on inner surface of an aspheric thin-walled crucible is achieved under a measurement area of 50 × 50 μm2. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance reveal that the content of Ce3+ increased from 28.54 to 43.76 %. Through Raman, XPS and Fourier transform infrared spectroscopy, CMP mechanisms are elucidated. Densified damaged layer on the surface of fused silica was induced by the transformation of surface structure from six-membered to four- or three-membered network. Ce-OH and Si-OH were formed between fused silica and ceria abrasives, forming Ce-O-Si by condensation reaction of dehydration. The developed green CMP and approach provide new pathway to polish and manufacture atomic surfaces for aspheric thin-walled crucibles with large diameters.

Structural, surface morphological and dielectric studies of guanidinium salt incorporated poly (ethylene oxide)/poly (vinyl pyrrolidone) solid polymer electrolytes

The research article investigates the effect of incorporating the guanidinium carbonate (GuC) salt into the poly vinylpyrrolidone (PVP) and polyethylene oxide (PEO) polymer matrix. Various weight percentages of GuC enriched PVP/PEO solid polymer electrolytes (SPEs) have been prepared by the simplest solution casting process. XRD analysis revealed that the incorporation of the GuC salt led to changes in the crystalline structure of the PVP/PEO. FTIR analysis confirms the presence of guanidinium carbonate in the blended polymeric system. FESEM imaging showed the uniform and smooth surface view of the electrolytes. DSC analysis suggests that the addition of the GuC led to a decrease in the melting temperature and an increase in the crystallisation temperature. The temperature-dependent dielectric analysis showed that the presence of the organic salt led to an increase in the dielectric constant of the polymer blend. Among all the prepared electrolytes, 25 wt.% GuC added polymer electrolyte achieved a higher conductivity of 3.00764 × 10−7 S/cm. Overall, the results of the study suggest that the incorporation of the GuC salt into the PVP/PEO can lead to significant changes in the structural, thermal, and dielectric properties of the blend. These findings have potential implications for the use of PVP/PEO blends in solid state battery applications.

A flexible high-efficiency approach to preparing a durable flame-retardant cellulosic fabric as well as the research of the property

This research aims to develop a durable and formaldehyde-free flame retardant treatment for cotton fabrics. Phosphorous acid (PA) is employed in conjunction with urea and guanidine carbonate to chemically bond the flame retardant to the cellulose fibers of the fabric. The treated fabrics are evaluated for their flame resistance, comfort, breathability, aesthetics, fire performance, carbon residue, limiting oxygen index, thermal stability, combustion behavior, and fabric properties. The results demonstrate successful grafting of PA onto cotton fabrics, leading to enhanced flame resistance while maintaining the desired fabric characteristics. The treated fabrics exhibit improved fire performance with increased carbon residue from 4.03% to 28.19% and higher LOI values from 18.0% to 43.5%. Moreover, the thermal stability of the fabric is enhanced, resulting in altered combustion behavior characterized by reduced the total heat release from 11.1 kJ/g to 0.1 kJ/g. Importantly, the flame-retardant treatment does not significantly impact the wettability or stiffness of the fabric. This study presents a simple and effective approach to produce highly efficient fire-resistant cotton fabrics, holding promise for various applications where fire safety is a concern.

Crystal structure and thermal behavior of three potential high-energy compounds of hydro-closo-borates with guanidinium

The novel guanidinium hydro-closo-borates featuring [BnHn]2– (n = 10 and 12) anions were successfully synthesized via the direct reaction of the corresponding free acids, (H3O)2[BnHn], with guanidinium carbonate, (CN3H6)2[CO3], in aqueous media. The resulting compounds crystallize in different monoclinic space groups such as C2/c, P2/c and P21/n for (CN3H6)2[B10H10], (CN3H6)2[B12H12] ⋅ 2 H2O and Cs(CN3H6)[B12H12], respectively. An intriguing aspect of these crystal structures was the observation of dihydrogen bonding interactions involving the negatively polarized hydrogen atoms of the boron clusters and the positively polarized hydrogen atoms in the guanidinium cations (Bδ+–Hδ–⋅⋅⋅Hδ+–Nδ–). Furthermore, a classical hydrogen bonding system is evident in (CN3H6)2[B12H12] ⋅ 2 H2O. The presence of negatively charged hydrogen (Hδ–) in hydroborate anions and positively charged hydrogen atoms (Hδ+) in guanidinium cations in these structures suggests their potential for facilitating H2 generation upon thermal decomposition. Furthermore, theoretical analysis predicts that under an oxygen atmosphere, diguanidinium dodecahydro-closo-hydroborate has the capacity to yield energy up to 11 MJ/mol.

Highly efficient separation of Nb from Ta using a unique solvent system containing tri-n-octyl phosphine oxide in an ionic liquid

The present investigation demonstrated the mutual separation Nb and Ta from their mixture in hydrochloric acid medium using TOPO in an ionic liquid (C6mim•NTf2). The maximum separation factor achieved was ∼ 4400. In C6mim•NTf2, the extraction proceeded via 'cation exchange' mechanism with MOCl2.TOPOIL+ as the species; while in n-dodecane the extraction proceeded via neutral 'solvation' mechanism with MOCl3.2TOPO as the extracted species (where, M = Nb and Ta). The sluggish extraction in C6mim•NTf2 was attributed to the its high viscosity coefficient compared to n-dodecane. The extraction was found to be spontaneous and exothermic in nature with a reduction in overall entropy indicating the formation of outer-sphere complexes. Dilute acid was found to be effective for the back extraction of Nb and Ta from the loaded n-dodecane phase, while EDTA - guanidine carbonate or DTPA - Guanidine carbonate were effective for back extraction from the ionic liquid phase. It was found that 2–3 contacts were sufficient for the quantitative back extraction of the metal ions. The C6mim•NTf2 based solvent systems exhibited better radiolytic stability compared to that of the n-dodecane based solvent system.

Highly efficient separation of Am(III) and Pu(IV) from lean feeds and soil using an extraction chromatographic resin containing a diglycolamide in an ionic liquid

A TODGA based extraction chromatographic resin containing an ionic liquid was used for the separation of actinide ions such as Am3+ and Pu4+ from samples such as lean effluents emanating from laboratory waste, environmental water as well as soil samples adjacent to a nuclear plant site. The methodology involved feed adjustment to 3 M HNO3 followed by conditioning of the column, loading, washing (3 M HNO3), and elution of the actinide ions. The elution of Am3+ was done using EDTA in a buffered medium (1 M guanidine carbonate) while that of Pu4+ was carried out using a mixture of 0.5 M oxalic acid and 0.5 M HNO3. The elution peaks were sharp with almost no tailing suggesting the efficiency of the separation method. The results obtained were compared with the literature results which suggested the high efficiency of the present method.

Guanidinium tetraborate anhydrate and its solid-state reaction synthesis

Guanidinium tetraborate anhydrate is formed as a new phase of guanidinium borate by heating the precipitate from the mixed solution of guanidinium carbonate and boric acid at 115–250°C. The new anhydrate phase is also formed by solid-state reactions of the powder mixture of guanidinium carbonate and boric acid at 115°C, and this route is advantageous over the liquid-phase method for industrial production. The structural and thermal properties of the new anhydrate phase are investigated using XRD and DTA-TG in comparison with the reported phase of guanidinium tetraborate dihydrate, [C(NH2)3]2[B4O5(OH)4]･2H2O. The chemical formula of the new phase is estimated to be [C(NH2)3]2[B4O5(OH)4]. This new anhydrate phase belongs to the monoclinic system, and the lattice constants are estimated at a = 0.7262 (9), b = 0.7868 (14), c = 0.5101 (9) nm, β = 87.61 (13)°, V = 0.2912 nm3, Z = 1 for the liquid-phase product, and a = 0.7250 (11), b = 0.7906 (21), c = 0.5083 (11) nm, β = 87.62 (14)°, V = 0.2911 nm3, Z = 1 for the solid-state reaction product.

Fluoride-free, simple, and environmentally friendly extraction of mixed oxides of niobium and tantalum from the Nigerian and Rwandan columbite-tantalite concentrates

We report a fluoride-free comparative study with promising results of an alkali-assisted roasting with KOH and water-based leaching of the Nigerian and Rwandan columbite-tantalite concentrates and application of guanidine carbonate to extract Nb and Ta as mixed oxides. The results proved that the alkali-assisted roasting the sample with KOH at optimum conditions, (250 °C, 100 % flux-to-concentrate ratio, 1 h), facilitated open-up of the (Nb–Ta)-minerals and induced their water solubilities. However, the Nigerian sample seems to be highly soluble relatively to the Rwandan sample. In all investigated cases, most of tin and iron in form of cassiterite and hematite and other impurities remained in the residue and their dissolutions decreased as temperature increased. Guanidine carbonate was used to extract both Nb and Ta dissolved in the pregnant leach solution of the Nigerian and Rwandan columbite-tantalite concentrate samples. The (Nb–Ta)-guanidine precipitate with purity of more than 95.0 % was recovered from leach liquor solution of −250 µm size fraction containing Nb (48.5 %), Ta (47.5 %), with Fe (2.6 %) and Mn (0.1 %) for N-Nass Con sample. For R-KMY Con sample, similar precipitate with purity of more than 94.0 % with chemical compositions of Nb (28.45 %), Ta (65.75 %) along with Fe (3.32 %) and Mn (0.77 %) was obtained from leach liquor of +250 µm size fraction. The amorphous (Nb–Ta)-guanidine precipitate was then calcined at 900 °C and converted the metals into their mixed oxides with high purity (more than 99%) and removed the guanidine as evidenced with their crystallographic peaks. The study presents a potential alternative to HF and promising opportunity for the sustainable extraction of Nb and Ta while the world is shifting toward clean energy.

Long-term antibacterial activity of guanidinium carbon dots without detectable resistance for the effective treatment of pneumonia caused by Gram-negative bacteria

The development of nanomedicine for the treatment of infection caused by resistant bacteria, especially Gram-negative bacteria, is still in the bottleneck. The long-term antibacterial activity and the low induced resistance risk need improvement. Herein, guanidinium-based carbon dots (G-CDs) were prepared from citric acid, dimethyldiallylammonium chloride, and polyhexamethyleneguanidine through melting strategy. The antibacterial properties of G-CDs against Gram-negative and resistant bacteria were investigated. G-CDs exhibit strong and long-term antibacterial activity, as well as antibiofilm activity, with less potential for inducing bacterial resistance. The antibacterial mechanism of G-CDs of the adsorption action and killing effect was elucidated, which was different from the mechanism of antibiotics. Moreover, derived from the interacting mode of nanomaterials and ssDNA, the enhanced ability of G-CDs against Gram-negative bacteria was studied based on the found interaction of G-CDs and lipopolysaccharide (LPS) for the understanding of the mode for the absorption of G-CDs on the cell wall of Gram-negative bacteria. The multimode interactions of van der Waals force, electrostatic adsorption and hydrogen bonding were clarified. Furthermore, G-CDs had excellent in vivo safety and in vivo therapeutic effects in E. coli-infected pneumonia through an intravenous approach. This study provides a hopeful strategy for developing antibacterial drugs from understanding the interacting mode of the drug and the cell wall of bacteria.

Waste Tire Derived Carbon Support for Non-Platinum-Group Metal Catalyst Materials for Oxygen Reduction Reaction in Alkaline Medium

A porous carbon material was synthesized using waste tire granules via pyrolysis. Six non-platinum-group metal catalyst materials were synthesized based on this carbon material, Fe(NO3)3 · 9H2O, and either dicyandiamide or guanidine carbonate as the nitrogen source. Synthesis parameters such as pyrolysis temperature, precursor mass ratios, and acid washing time were varied for each material. All catalysts were characterized physically using HR-SEM, SEM-EDX, and N2 sorption analyses as well as electrochemically using the rotating disk electrode method in 0.1 M KOH. The materials were rich in nanofibers, and exhibited moderate porosity and specific surface area (S BET = 77-194 m2 g-1). By modifying the synthesis parameters of the materials, the electrochemical properties were successfully improved, achieving E onset = 0.92 V vs RHE and E 1/2 = 0.82 V vs RHE (Fe-guan III 900). The number of transferred electrons in the ORR was n = 4 for the more active materials.

Growth and characterization of Oxalic acid doped Guanidine carbonate (OGC) single crystal

Oxalic acid doped Guanidine carbonate, an organic nonlinear optical single crystal is developed successfully by slow evaporation solution growth method using deionized water as a solvent. The crystal structure and lattice parameters of grown crystals are determined by single crystal X – ray diffraction of the grown crystal. The presence of expected functional groups of the grown crystal is identified by Fourier Transform Infrared spectroscopy. The optical transmittance spectrum of the crystals has been recorded by UV –Vis-NIR spectral analysis. The calculated large bandgap of the grown crystals attests them for optoelectronic applications. The Thermo Gravimetric and Differential Thermal analyses have been carried out to understand the thermal responses of the crystals. Second harmonic generation efficiency of the grown crystals have been calculated by Kurtz powder method. Nd – YAG laser (1064 nm) was used to find out the laser damage threshold of the grown crystal. The inspiring results confirms that the grown crystal serve as a potential candidate for photonic devices.

Effective and Efficient Porous CeO2 Adsorbent for Acid Orange 7 Adsorption.

A porous CeO2 was synthesized following the addition of guanidine carbonate to a Ce3+ aqueous solution, the subsequent addition of hydrogen peroxide and a final hydrothermal treatment. The optimal experimental parameters for the synthesis of porous CeO2, including the amounts of guanidine carbonate and hydrogen peroxide and the hydrothermal conditions, were determined by taking the adsorption efficiency of acid orange 7 (AO7) dye as the evaluation. A template-free hydrothermal strategy could avoid the use of soft or hard templates and the subsequent tedious procedures of eliminating templates, which aligned with the goals of energy conservation and emission reduction. Moreover, both the guanidine carbonate and hydrogen peroxide used in this work were accessible and eco-friendly raw materials. The porous CeO2 possessed rapid adsorption capacities for AO7 dye. When the initial concentration of AO7 was less than 130 mg/L, removal efficiencies greater than 90.0% were obtained, achieving a maximum value of 97.5% at [AO7] = 100 mg/L and [CeO2] = 2.0 g/L in the first 10 min of contact. Moreover, the adsorption-desorption equilibrium between the porous CeO2 adsorbent and the AO7 molecule was basically established within the first 30 min. The saturated adsorption amount of AO7 dye was 90.3 mg/g based on a Langmuir linear fitting of the experimental data. Moreover, the porous CeO2 could be recycled using a NaOH aqueous solution, and the adsorption efficiency of AO7 dye still remained above 92.5% after five cycles. This study provided an alternative porous adsorbent for the purification of dye wastewater, and a template-free hydrothermal strategy was developed to enable the design of CeO2-based catalysts or catalyst carriers.

Growth parameters and investigations on the structural, optical, mechanical, thermal and electrical properties of an l-proline guanidine carbonate single crystal

Single crystal of l-proline guanidine carbonate (LPGC) was grown by adapting most important method of slow evaporation technique by using double distilled water as a solvent at room temperature. Single crystal X-ray diffraction determined that the crystal structure of LPGC as orthorhombic non-centro symmetric system with the P212121 space group and the lattice parameters are confirmed to be a = 8.3580(4) Å, b = 10.3479(4) Å, c = 15.1833(5) Å, α = β = γ = 90°, Volume V = 1313.17(9) A3. The diffraction pattern of powder X-ray diffraction describes the factors of the crystallinity nature and the purity of the LPGC crystal. The optical absorption spectrum of LPGC crystal has been recorded and the linear optical constants such as the absorption coefficient (α), Energy band gap (Eg), extinction coefficient (K), refractive index (n) and Urbach energy (Eu) have been calculated. The active functional groups of the grown crystal were identified and confirmed by Fourier transform infrared spectroscopic study (FTIR) and Fourier transform Raman spectroscopy (FT-RAMAN). The thermal behavior and the thermal stability of the crystal were investigated by the thermogravimetric-differential thermal analysis (TG-DTA). Vickers micro hardness test was carried out to determine the mechanical stability and the hardness parameters of the crystals such as stiffness constant (C11), yield strength (σy), hardness number (Hv) and work hardening coefficient (n). The luminescence activity of the grown crystal was determined by the photoluminescence (PL) spectroscopy. The dielectric properties of the LPGC crystal were analyzed at various temperature and frequency. The presence of active chemical compounds in LPGC crystal was confirmed by energy dispersive analysis (EDAX). The Z-scan analysis of the grown crystal determines the Q-switching behavior of the grown LPGC crystal.

Ultra-fast microwave regeneration of CO2 solid sorbents for energy-efficient direct air capture

Large-scale deployment of direct air capture (DAC) technologies has become critical for mitigating climate change. Towards this end, energy-efficient regeneration of the sorbents used in the process of carbon capture from air is very important to significantly reduce the high operational cost of DAC. Guanidine compounds can be used with environmentally friendly aqueous amino acids (e.g., potassium sarcosinate) for fast and effective CO2 capture from air, and have a strong potential for low-energy CO2 release and sorbent regeneration. In this process, the amino acid absorbs the CO2 from the air, and the guanidine compounds react with the CO2-rich amino acid solution and crystallize as an insoluble carbonate salt. Separation and thermal regeneration of the precipitated guanidine carbonate salt leads to an overall low-temperature and low-energy direct air capture process. Effective CO2 release from the solid guanidine compound can be achieved by mild heating at 120 °C. In this study, to overcome the relatively inefficient traditional conductive heating of the crystalline solid (i.e., Methylglyoxal-bis(iminoguanidine) carbonate, MGBIG carbonate), we evaluated the feasibility of microwave heating of MGBIG carbonate in terms of power requirement, radiation time, and solids mass for efficient CO2 desorption. The energy consumption needed by a microwave oven and a conventional oven to regenerate the same mass of the sorbent was directly measured to compare the total energy required per unit mass of regenerated sample and provide an understanding of the potential benefits of microwave regeneration. We found that microwave heating effectively regenerates MGBIG carbonate, which may be facilitated by the water molecules that are co-crystallized with carbonate in the guanidine crystals. Microwave heating at 2.54 GHz with 1250 W is up to 17 times faster than conventional conductive heating at 160 °C, resulting in 40 % electrical energy reduction. These results indicate that microwave regeneration may be an energy-efficient method for fast regeneration of solid sorbents used for direct air capture.

Comparative Effects of Graphitic Carbon Nitride Precursors on the Photocatalytic Degradation of Pyrene

Pyrene is a ubiquitous, persistent, and mutagenic pollutant that belongs to the polycyclic aromatic hydrocarbons. Graphitic carbon nitride (g-C3N4) has emerged as a promising photocatalyst for degradation of various pollutants in water and wastewater treatment due to its unique band structure and excellent physiochemical stability. This paper presents the comparative study of composites g-C3N4 from various combinations of precursors using thermal polycondensation at 600 °C. Comparative experiments revealed that the preparation conditions of both precursors and the mass ratios of precursor influenced the overall performance of photocatalyst during photocatalytic degradation of pyrene. Experimental results indicated that the best performance of composites g-C3N4t photocatalyst was prepared from a wet mixture of dicyandiamide and guanidine carbonate precursors at a mass ratio of 1:1 with 43.9 % pyrene degradation under visible light irradiation for 240 mins. The reusability of the best g-C3N4 composites for the photocatalytic degradation of pyrene was also investigated. It was found that the prepared photocatalyst was stable up to five cycles of photocatalysis. Meanwhile, holes (h+) and hydroxyl radicals (·OH) were identified as the primary and secondary dominant reactive species in the photocatalytic degradation through scavenging trapping experiments.