Chemical Science International Journal

Thermal Stability of Ammonium Nitrate: A Critical Narrative Review

2026-07-06T11:10:20+00:00

Ammonium nitrate is a simple inorganic salt with a complex safety profile. It is essential to fertiliser production and has important uses as an oxidising component in explosives and propellant systems, yet its decomposition behaviour has contributed to some of the most damaging industrial accidents of the past century. This review examines the thermal stability of ammonium nitrate across crystal polymorphism, decomposition chemistry, heat and mass transfer, additives, contamination, engineered stabilisation, energetic formulation and process-safety practice. The central argument is that thermal stability is not a fixed property that can be represented by one onset temperature or one activation-energy value. It is an observed behaviour that depends on composition, moisture, acidity, impurity profile, physical form, heating rate, atmosphere, gas exchange, confinement, scale and storage history. Recent thermal-analysis studies have clarified how chlorides, acids, pyrite, rust, transition-metal species and some organic contaminants can reduce the stability margin, while selected phosphates, carbonates, magnesium compounds, sulphates, urea and mineral additives may inhibit decomposition under defined conditions. Newer materials-design approaches, including phase-stabilised ammonium nitrate, metal-organic frameworks, zeolitic imidazolate frameworks, ferrites, coordination complexes and energetic co-crystals, show that crystal chemistry and catalytic architecture can be used to reshape phase transitions and decomposition pathways. These advances, however, must be interpreted carefully: a formulation that performs well in a propellant is not necessarily safer for bulk storage. The review concludes that safe use of ammonium nitrate depends on compatible formulation, strict contamination control, ventilation, inventory management, fire prevention and cautious translation of laboratory data to real storage and emergency scenarios.

A Critical Review on the Design, Synthesis and Applications of Carbene Superbases

2026-07-11T11:43:57+00:00

Carbenes, once regarded as fleeting reactive intermediates, have matured into one of the most versatile families of neutral organic bases known to chemistry. Within the last two decades, judicious modification of the carbene framework has produced species whose basicity rivals and, in several instances, surpasses that of the classical phosphazene and guanidine superbases, giving rise to the emerging concept of the carbene superbase. This review provides a critical appraisal of the structural principles that confer exceptional Brønsted basicity on singlet carbenes, tracing the progression from N-heterocyclic carbenes through cyclic (alkyl)(amino)carbenes, mesoionic and abnormal carbenes, to the doubly donating carbodicarbenes and related carbones. Synthetic strategies for accessing these species, including deprotonation of azolium and iminium precursors, reductive routes, and substituent-tuning approaches that stabilise the free carbene while preserving its basicity, are discussed and compared. The applications of carbene superbases are then examined across four principal domains: organocatalysis through Breslow-intermediate and Brønsted-base pathways, metal-free ring-opening polymerisation, ligand design for transition-metal and main-group catalysis, and small-molecule activation through frustrated Lewis pair chemistry, with additional consideration of emerging materials and biomedical applications. Throughout, the basicity, nucleophilicity, and steric parameters that govern reactivity are related to measurable spectroscopic and thermodynamic descriptors. The review closes with a discussion of unresolved mechanistic questions, prospects for further tuning of carbene basicity, and the practical limitations that continue to constrain the wider deployment of these reagents outside specialist laboratories.

Preparation of High-Surface-Area Carbon Adsorbents from Plum Seed Pods Via Thermochemical Activation

2026-06-26T12:31:31+00:00

Activated carbon is among the most widely used adsorbent materials because of its high specific surface area, developed pore structure, chemical stability, and capacity to adsorb various organic and inorganic pollutants. This study aimed to prepare and characterise activated carbon adsorbents from plum seed shells through thermochemical activation using KOH and NaOH as activating agents. Activated carbon adsorbents were prepared from plum seed shells by carbonisation followed by thermochemical activation with potassium hydroxide and sodium hydroxide. The raw biomass was washed, dried, crushed, carbonised at 500 °C, and subsequently activated under different alkali-treatment conditions. The prepared carbon materials were washed, neutralised, dried, and characterised using nitrogen adsorption–desorption analysis, BET surface area measurement, t-Plot and BJH methods, benzene vapour adsorption, scanning electron microscopy with energy-dispersive X-ray analysis, Fourier-transform infrared spectroscopy, and X-ray diffraction analysis. The untreated plum seed shell showed a very low BET surface area of 1.3444 m²/g, whereas carbonisation at 500 °C increased the surface area to 84.2376 m²/g. Steam activation further increased the BET surface area to 542.8618 m²/g. Among the chemically activated samples, the KOH-activated carbon prepared at a carbonizate-to-KOH ratio of 1:0.05 showed the highest BET surface area of 944.2450 m²/g, micropore surface area of 728.0441 m²/g, total pore volume of 0.497989 cm³/g, and micropore volume of 0.383966 cm³/g. Benzene vapour adsorption measurements also showed improved adsorption performance, with the highest adsorption capacity of 3.660 mmol/g and a benzene-derived surface area of 881.24 m²/g for the same sample. SEM observations confirmed the formation of irregular porous surfaces, while FTIR and XRD analyses indicated structural transformation towards a predominantly amorphous carbonaceous material. The results show that plum seed shells can be converted into porous activated carbon adsorbents, with KOH activation providing better textural and adsorption properties than NaOH activation under the studied conditions.

Industrial Evaluation of Activated Navbahor and Nurota Bentonites as Locally Sourced Media for the Finishing Stage of Kerosene Demercaptanization

2026-07-02T04:57:42+00:00

This study evaluated activated bentonites from the Navbahor and Nurota deposits in Navoiy Province, Uzbekistan, as locally sourced media for the finishing stage of kerosene demercaptanization. The materials were assessed as alternatives to imported ATTA PULGUS clay in the clay-filter section of a MERICAT II fibre-film demercaptanization unit. The investigation comprised chemical characterisation, bulk-density measurement before and after thermal pretreatment, and assessment of fuel-quality parameters against OʻzDSt 1117:2007 using prescribed standard methods. Compared with the imported reference, activated Navbahor bentonite was silica–alumina dominated but contained less silica and alumina and more calcium, iron, and sulphate. Calcination at 500 °C for 6 h reduced the bulk density of Navbahor bentonite from 0.850 to 0.812 g/cm³ and that of Nurota bentonite from 0.940 to 0.890 g/cm³. In a 100 kg pilot loading, activated Navbahor bentonite improved Saybolt colour from +15 to +22 points, reduced specific electrical conductivity from 6 to 1 pS/m, and lowered mercaptan sulfur from 0.0018 to 0.001 wt.%, while copper-strip corrosion remained at Class 1. In the comparative industrial trial, kerosene treated with both activated local bentonites showed conductivity of 1 pS/m, mercaptan sulfur of 0.0017 wt.%, copper-strip corrosion of Class 1, and Saybolt colour of +15 points. The results indicate that activated Navbahor and Nurota bentonites provided technically acceptable polishing performance under the studied operating conditions.

Physical and Mechanical Properties of Np-Fertilizers Derived from Ammonium Nitrate and Guliob Phosphorite

2026-07-02T05:04:22+00:00

This study examined the production of NP fertilisers by incorporating Guliob phosphorite (GP) into molten ammonium nitrate (AN) at AN weight ratios ranging from 99.5:0.5 to 65:35. The phosphorite-nitrate melt was granulated by prilling, and the chemical composition and selected physicochemical properties of the resulting products were evaluated. Increasing GP content decreased total nitrogen from 34.74% to 22.73%, whereas total P2O5 and CaO increased from 0.052% to 3.673% and from 0.12% to 10.31%, respectively. The interaction of GP with the AN melt at 170-175°C promoted partial activation of phosphate and calcium compounds, increasing the proportion of assimilable P2O5 and CaO. The most suitable compositions were identified as AN = 97.5:2.5 for non-caking AN and AN = 80:20 for thermally stabilised nitrate. These samples contained Ntotal., P2O5total. and CaOtotal. at 34.05%, 0.24% and 0.69%, and 28.0%, 2.05% and 5.90%, respectively. Their granule strengths were 4.09 and 9.69 MPa, exceeding that of conventionally produced magnesite-modified ammonium nitrate (1.58 MPa). GP addition also reduced adhesion, porosity and diesel fuel absorption, indicating improved structural density and handling safety. The findings show that GP can function as both a phosphate-bearing additive and a structural modifier for producing NP fertilisers with improved physical and mechanical properties.

Investigation of Phase Equilibria and Polythermal Solubility in the MgCl₂–NaCl–H₂O System for the Extraction of Magnesium-Bearing Raw Materials from Natural Brines

2026-07-02T11:08:15+00:00

Natural brines are potential sources of magnesium-bearing raw materials, but their effective utilisation requires an understanding of salt–water phase equilibria and crystallisation behaviour. This study investigated phase equilibria and polythermal solubility in the MgCl₂–NaCl–H₂O system and evaluated natural brine from the Kuyimazor area of Kogon district, Bukhara region, Uzbekistan, as a possible source of magnesium-containing products. Model solutions containing magnesium chloride, sodium chloride, and water were examined by the visual polythermal method over the temperature range from −35.6 to −3.0 °C. Polythermal solubility diagrams and internal sections were constructed to identify crystallisation regions and phase-transition behaviour. The natural brine and crystallised salt products were characterised by standard chemical analysis, X-ray fluorescence spectroscopy, scanning electron microscopy with energy-dispersive spectroscopy, elemental mapping, and Fourier-transform infrared spectroscopy. Magnesium recovery was also examined by alkaline precipitation using sodium hydroxide solution. The constructed diagram indicated crystallisation regions corresponding to ice, NaCl, NaCl·2H₂O, MgCl₂·12H₂O, MgCl₂·8H₂O, and MgCl₂·6H₂O. Characteristic phase-transition temperatures were observed at approximately −35.6, −34.6, −20.6, −17.0, −4.4, and −3.0 °C. XRF analysis showed that the investigated salt sample contained 16.5 mass% Mg. The results showed that increasing magnesium chloride concentration reduced sodium chloride solubility, indicating a salting-out effect that may support magnesium enrichment in the liquid phase. XRF and SEM–EDS analyses showed that sodium, magnesium, chlorine, and oxygen were the dominant components of the studied salt materials. FTIR spectra confirmed the hydrated nature of the crystallised phases and indicated the formation of hydroxyl-containing magnesium precipitate after alkaline treatment. The findings provide physicochemical information relevant to the selective recovery of magnesium-bearing materials from local natural brines.

Antioxidant Activity of Extracts and HPLC-DAD-MS Identification of the Major Anthocyanins of the Fruit Peel of Spondias purpurea L. (Anacardiaceae) in Burkina Faso

2026-07-03T07:09:15+00:00

Spondias purpurea L. is an Anacardiaceae fruit species whose peel may contain phenolic pigments of interest, although its phytochemical profile remains insufficiently documented in Burkina Faso. This study evaluated the anthocyanin, phenolic compound and antioxidant contents of the fruit peel and identified the major anthocyanins present. Fresh peel extracts were prepared using acidified methanol and an ethanol-water solvent system. Total anthocyanins were determined by the differential pH method, phenolic compounds by the Folin-Ciocalteu method and antioxidant content by the FRAP assay. Structural identification was performed using HPTLC and HPLC-DAD-MS-visible UV analysis after extraction and acid hydrolysis. The acidified methanol extract contained 7.50 mg cyanidin 3-glucoside equivalents per 100 g of fresh plant material. The phenolic compound and antioxidant contents of the acidified methanol extract were 7.63 mg GAE/g and 6.0 mg TE/g of fresh plant material, respectively, whereas the ethanol-water extract gave lower values. HPLC-DAD-MS analysis indicated three major anthocyanins: peonidin-3-O-galactose, pelargonidin-3-O-glucose and peonidin-3-O-malonoylrhamnose. These results indicate that the fruit peel contains anthocyanins and antioxidant-associated phenolic compounds. Pending structural confirmation by NMR, the peel may be considered a potentially useful plant material for further phytochemical evaluation rather than being treated only as waste.

Phytochemical Profiling, LC–ESI–QTOF–MS/MS Characterization, and Antioxidant Potential of Hydroethanolic Leaf Extracts of Pericopsis laxiflora

2026-07-04T10:39:41+00:00

Pericopsis laxiflora (Fabaceae) is an ethnomedicinal plant widely used in African traditional medicine for the management of inflammatory disorders, fever, gastrointestinal disturbances and liver-related diseases. Despite its therapeutic importance, detailed information on the phytochemical composition of its leaves remains limited. This study investigated the phytochemical profile, characterised secondary metabolites using liquid chromatography-electrospray ionisation quadrupole time-of-flight tandem mass spectrometry (LC-ESI-QTOF-MS/MS), and evaluated the antioxidant potential of hydroethanolic leaf extracts of P. laxiflora collected in Korhogo, Côte d’Ivoire. Qualitative phytochemical screening revealed the presence of tannins, flavonoids, coumarins, alkaloids, anthocyanins, sterols and terpenoids. Quantitative analysis showed high levels of total polyphenols (627.20 ± 50.37 mg GAE/g DW) and condensed tannins (162.65 ± 4.78 mg CE/g DW), together with a moderate flavonoid content (7.20 ± 0.48 mg QE/g DW). Antioxidant activity evaluated using the DPPH radical scavenging assay demonstrated considerable antiradical activity, with an IC₅₀ value of 0.051 ± 0.002 mg/mL, compared with vitamin C (IC₅₀ = 0.015 ± 0.00021 mg/mL). LC-ESI-QTOF-MS/MS analysis tentatively characterised twelve metabolites belonging to different chemical classes, including flavonoid glycosides (rutin), flavonoids (quercetin, kaempferol and luteolin), isoflavonoids (angolensin, genistein, formononetin, afrormosin and pisatin), condensed tannins (procyanidin), alkaloids (N-methylcytisine) and cyanogenic glycosides (lotaustralin). Several compounds are reported here for the first time in P. laxiflora leaves. These findings support the traditional medicinal use of P. laxiflora and suggest that its leaves may constitute a source of bioactive compounds with potential pharmaceutical relevance. However, further toxicological and pharmacological studies are required to establish their safety and therapeutic potential.

Synthesis, Characterization and Application of a Tetraethoxysilane–Stearic Acid Organic–Inorganic Hybrid Hydrophobizing Agent for the Water Protection of Porous Construction Materials

2026-07-06T12:44:47+00:00

Aims: The study aims to synthesise, structurally characterise and evaluate an organic–inorganic hybrid hydrophobizing agent derived from tetraethoxysilane (TEOS) and stearic acid for the long-term water protection of porous construction materials, and to verify its performance against national and interstate standards.

Study Design: Laboratory synthesis of the agent followed by spectroscopic (FTIR) and thermal (TGA–DTG–DSC) characterisation, qualitative wettability testing, and standardised quantitative determination of the water-protection efficiency on real construction products.

Place and Duration of Study: The study was conducted at Department of Chemical Technology, Bukhara State Technical University; standardised testing at the “Uz Test” State Institution (Bukhara branch) of the Uzbek Agency for Technical Regulation and the Bukhara Special Testing Construction Laboratory LLC.

Methodology: The hybrid agent was prepared from TEOS and stearic acid by an acid-catalysed sol–gel route, using sodium peroxide (Na₂O₂) as an oxidising/water-releasing promoter and sulfuric acid (H₂SO₄) as the condensation catalyst (60–80 °C, 6–7 h). The molecular architecture was probed by Fourier-transform infrared spectroscopy (FTIR) and the thermal behaviour by simultaneous thermogravimetric–differential thermal analysis (TGA–DTG–DSC). The agent was brush-applied to fired-clay (ceramic) brick and concrete, and the hydrophobization efficiency was determined in two accredited laboratories in accordance with O’zMSt 705:2025, GOST 7025-91 and GOST 12730.2-2020.

Results: FTIR confirmed a genuine organic–inorganic hybrid in which a condensed siloxane (Si–O–Si) network derived from TEOS coexists with long aliphatic chains and reactive silanol (Si–OH) groups derived from stearic acid. Thermal analysis revealed high thermal stability: only ≈2% of the mass was lost below 150 °C, the functional organic component decomposed above ≈200 °C, and a thermally robust inorganic residue of ≈52% remained, corroborating the silica-rich framework. The treated products carried discrete, spherical water droplets; the hydrophobization efficiency reached 79.0–79.1% for fired-clay brick and 80.4–81.6% for concrete, all conforming to the cited standards.

Conclusion: Combining a TEOS-derived silica backbone with hydrophobic fatty-acid chains affords an effective water repellent for porous construction materials. Its water-protection performance was verified by accredited, standards-based testing, while the fluorine-free formulation based on locally available raw materials offers potential economic and environmental advantages that merit further dedicated evaluation.

Synthesis and High-resolution Mass Spectrometric Elucidation of a Novel Symmetrical N,N′-Hexamethylene Bis-Thiourea Derivative

2026-07-07T11:45:16+00:00

Aims: This study aimed to synthesise and elucidate a novel symmetrical bis-thiourea derivative, N,N′-hexamethylene bis[borneoylcarbamate] N,N′-bis(phenylthiourea), obtained from N,N′-hexamethylene bis[borneoylcarbamate] and phenyl isothiocyanate. Study Design: An experimental synthetic organic chemistry study was conducted to optimise solvent, catalyst, reaction time and temperature for improving the isolated product yield and confirming the structure of the target compound.

Place and Duration of Study: The work was carried out in the Department of Chemical Technology, Navoi State University of Mining and Technologies, Uzbekistan, between January and July 2025.

Methodology: The biscarbamate precursor (0.0025 mol, 1.11 g) was reacted with phenyl isothiocyanate (0.0050 mol, 0.676 g) in the presence of triethylamine in N,N-dimethylformamide. Reaction conditions were varied using different solvents, base catalysts, reaction times and temperatures from 0°C to 60°C. The isolated crystalline product was purified by recrystallisation and examined using thin-layer chromatography, ATR-FTIR spectroscopy and high-resolution electrospray ionisation mass spectrometry in positive-ion mode.

Results: The highest isolated yield, 62.2%, was obtained at 30°C after 6 h in DMF with triethylamine. Lower temperatures gave reduced yields, whereas temperatures above 30°C decreased the yield from 58% at 40°C to 48% at 60°C. FTIR analysis showed disappearance of the precursor carbamate ester C=O band near 1730 cm⁻¹ and the appearance of a diagnostic ν(C=S) band at 632 cm⁻¹. HR-ESI-MS gave a dominant fragment at m/z 476.27848, assigned to [C28H35N4O3]+, with a mass error of 0.26 mDa (0.55 ppm).

Conclusion: The results support the formation of the proposed symmetrical bornyl-functionalised bis-thiourea under mild reaction conditions.

Phase Equilibria and Solubility Diagram in the Ternary System Sodium Hypochlorite – potassium Chlorate – water

2026-07-09T08:59:37+00:00

Phase equilibria and solubility in the NaClO–KClO₃–H₂O ternary system were investigated over the temperature range from −21 to +18 °C using the visual-polythermal method. Based on experimental data obtained for the boundary binary systems and five internal sections, a complete polythermal solubility diagram was constructed. The diagram reveals the crystallization fields of ice, potassium chlorate, sodium chloride, sodium hypochlorite pentahydrate (NaClO•5H₂O), sodium hypochlorite sesquihydrate (NaClO•2.5H₂O), and anhydrous NaClO. It was established that the system belongs to a simple eutectic type, with no formation of new chemical compounds or solid solutions within the investigated range. A pronounced salting-out effect of sodium hypochlorite on potassium chlorate was observed, leading to a significant decrease in KClO₃ solubility with increasing NaClO concentration. The obtained results provide a physicochemical basis for optimizing crystallization processes and developing efficient chlorate-based defoliant formulations.

Production, Characterization and Performance Evaluation of Modified Crab Shell Chitosan for Sustainable Coagulation of Abattoir Wastewater

2026-07-11T11:48:02+00:00

Abattoir wastewater is among the most heavily polluted agro-industrial effluents, and conventional coagulants such as alum and ferric chloride raise concerns regarding residual metal toxicity and non-biodegradable sludge. This study developed a chitosan-based coagulant derived from crab shell waste and cross-linked with epichlorohydrin (CL-CS) for sustainable abattoir wastewater treatment. Extraction was optimised using a Box-Behnken design, achieving a degree of deacetylation of 88.2% at 50% NaOH and 120 °C. FTIR, XRD, TGA, BET and zeta potential analyses confirmed successful deacetylation and cross-linking, with CL-CS exhibiting reduced crystallinity (38.2%), higher surface area (24.3 m²/g), improved thermal stability (Tpeak = 315 °C) and stronger cationic charge (+41.7 mV at pH 6) than native chitosan. Coagulation was optimised using a central composite design, yielding 92.7% turbidity removal and 78.8% COD removal at a 60 mg/L dose, pH 4.0, 250 rpm rapid mixing, 40 rpm slow mixing and 60 min settling time (R² = 0.985). Coagulation followed second-order kinetics (K = 5.84 × 10⁻⁴ NTU⁻¹ min⁻¹), with a floc fractal dimension of 2.34, indicating dense, polymer-bridged aggregates. CL-CS outperformed alum and ferric chloride in turbidity, COD, TSS and oil/grease removal, while producing the lowest sludge volume (41.8 mL/L), leaving no residual metal contamination and achieving the lowest unit treatment cost ($0.079/m³). Pearson correlation confirmed the degree of deacetylation and zeta potential as the strongest predictors of performance (r > 0.91). These findings indicate that CL-CS is a promising low-cost and environmentally sustainable alternative to conventional coagulants for abattoir wastewater treatment.