Influence of CaCl2 on the hydrothermal modification of Mg(OH)2

The influence of CaCl₂ on the hydrothermal modification of Mg(OH)₂ was investigated in this paper. The experimental results indicated that dispersive Mg(OH)₂ hexagonal plates with the regular shape, the enlarged size and the perfect crystallinity were formed by treating the irregular Mg(OH)₂ agglomerates at elevated temperatures in dilute CaCl₂ solutions. Thermodynamic analysis showed that the presence of CaCl₂ at the elevated temperature promoted the formation of MgOH⁺, which was favorable for the formation of Mg(OH)₆⁴⁻ and the growth of Mg(OH)₂ crystals.     

热重分析法研究氢氧化镁纳米粉体的非等温分解动力学

以白云石为原料,盐酸酸溶后得到CaCl₂-MgCl₂滤液,采用氨水直接沉淀法制备出符合HG/T 3607-2000Ⅰ型标准的六方片状的纳米氢氧化镁。六方片厚度为25～30 nm,直径为0.3～0.4 mm。利用热重分析法对纳米氢氧化镁在不同升温速率下的热分解动力学进行研究,以期深入了解纳米氢氧化镁热分解制备纳米氧化镁粉体过程的物理化学本质。采用Kissinger法和Ozawa法计算出氢氧化镁热分解反应活化能分别为115.47 kJ·mol^-1和126.04 kJ·mol^-1。对热重分析数据进行处理和拟合,判断纳米氢氧化镁粉体热分解反应机理函数为Avrami-Erofeev（n=1.5）的随机成核和随后生长机理。指前因子为3.077×10¹⁰ s^-1。纳米氢氧化镁经煅烧制备得到的氧化镁纳米球的直径为80～100 nm。     

The encapsulation of Mg(OH)2 sludge in composite cement

A range of magnesium hydroxide waste sludges arising from the re-processing of nuclear fuel exist in the UK and require safe long-term disposal. Similar wastes undergo a cementation process in order to immobilise radioactive material prior to disposal. Simulant magnesium hydroxide sludges have been prepared and their subsequent interactions with composite cement systems based on the partial replacement of ordinary Portland cement with blastfurnace slag and pulverised fuel ash have been studied. This work has concluded that there was little reaction between the sludge and any of the composite cements during hydration. Apart from a small quantity of a hydrotalcite-type phase containing magnesium from the sludge, the main phases detected were C-S-H and unreacted brucite. This indicates that the magnesium in the sludges is encapsulated by the cement, rather than being immobilised or chemically bound within the hardened matrix.     

Preparation and characterization of CaO nanoparticles from Ca(OH)2 by direct thermal decomposition method

CaO is an important material because of its application as catalyst and effective chemisorbents for toxic gases. In this research CaO nanoparticles were prepared via direct thermal decomposition method using Ca(OH)₂ as a wet chemically synthesized precursor. Nanocrystalline particles of Ca(OH)₂ have been obtained by adding 1 and 2 M NaOH aqueous solutions to 0.5 M CaCl₂·2H₂O aqueous solutions at 80 °C. The precursor [Ca(OH)₂] was calcined in N₂ atmosphere at 650 °C for 1 h. Samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), infrared spectrum (IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunaure–Emett–Teller (BET). SEM images showed that CaO nano-particles were nearly spherical in morphology. TEM images illustrated that produced CaO nano-particles had the mean particle size of 91 and 94 nm for 1 and 2 M NaOH concentration, respectively. As a result, this method could be used for production of CaO nano-particles on large-scale as a cheap and convenient way, without using any surfactant, organic medium or complicated equipment.     

Hydrothermal mass production of MgBO2(OH) nanowhiskers and subsequent thermal conversion to Mg2B2O5 nanorods for biaxially oriented polypropylene resins reinforcement

Mass production of one-dimensional (1D) nanomaterials has emerged as one of the most significant challenges in powder technology. In this contribution, MgBO₂(OH) nanowhiskers were hydrothermally produced at a kilogram scale in a 150 L stainless steel autoclave at 200 °C for 12.0 h by using MgCl₂·6H₂O, H₃BO₃ and NaOH as the raw materials. The subsequent thermal conversion of the MgBO₂(OH) nanowhiskers at 700 °C for 6 h led to 3.75 kg of high crystallinity monoclinic Mg₂B₂O₅ nanorods, with a length of 0.47-1.3 µm, a diameter of 55-160 nm, and an aspect ratio of 3-15. After the nanorods have been surface modified with the silane coupling agent KH-550, the reinforcing and toughening effects of the Mg₂B₂O₅ nanorods on the biaxially oriented polypropylene resins (BOPP-D1) were evaluated. The filling of the Mg₂B₂O₅ nanorods into the resins resulted in the increase in the tensile strength, the impact strength, and the melt flow index of the BOPP-D1 composites. The appropriate ratio of coupling agent to fillers (Mg₂B₂O₅ nanorods) and the ratio of fillers to resins were determined within the range of 0.6-1.2 wt.% and 8-15 wt.%, respectively. The optimal ratio of fillers to resins was ca. 10 wt.%. The present mass production of MgBO₂(OH) nanowhiskers and Mg₂B₂O₅ nanorods is believed to be helpful for enlarging and propelling the applications of the 1D magnesium borate nanostructures in the near future.     

利用氢氧化镁热分解氯化铵制氨气工艺的研究

对利用氢氧化镁热分解氯化铵制氨气反应体系进行了热力学计算分析,以反应温度、反应物的物质的量比、反应时间为变量,以固体产物中的含氮量、氯收率以及氨气收率等为评价指标,对氢氧化镁热分解氯化铵制氨气的工艺条件进行了研究。实验结果表明,在反应温度为375 ℃,氢氧化镁与氯化铵的物质的量比为1∶0.75,反应时间为50 min时,氯收率和氨气收率均可达到90%以上,同时氢氧化镁分解氯化铵能够直接生成碱式氯化镁,不需向反应器中通入水蒸气。     

Preparation and crystallization kinetics of micron-sized Mg(OH)2 in a mixed suspension mixed product removal crystallizer

Magnesium hydroxide is an important chemical, and is usually obtained from seawater or brine via precipitation process. The particle size distribution of magnesium hydroxide has great effects on the subsequent filtration and drying processes. In this paper, micron-sized magnesium hydroxide with high purity, large particle size and low water content in filter cake was synthesized via simple wet precipitation in a mixed suspension mixed product removal (MSMPR) crystallizer. The effects of reactant concentration, residence time and impurities on the properties of magnesium hydroxide were investigated by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Malvern laser particle size analyzer. The results show that NaOH concentration and residence time have great effects on the water content and particle size of Mg(OH)₂. The spherical Mg(OH)₂ with uniform diameter of about 30 μm was obtained with purity higher than 99% and water content less than 31%. Furthermore, the crystallization kinetics based on the population balance theory was studied to provide the theoretical data for industrial enlargement, and the simulation coefficients (R²) based on ASL model and C-R model are 0.9962 and 0.9972, respectively, indicating that the crystal growth rate of magnesium hydroxide can be well simulated by the size-dependent growth models.     

Hydrothermal transformation of the calcium aluminum oxide hydrates CaAl2O4·10H2O and Ca2Al2O5·8H2O to Ca3Al2(OH)12 investigated by in situ synchrotron X-ray powder diffraction

The hydrothermal transformation of calcium aluminate hydrates were investigated by in situ synchrotron X-ray powder diffraction in the temperature range 25 to 170 °C. This technique allowed the study of the detailed reaction mechanism and identification of intermediate phases. The material CaAl₂O₄·10H₂O converted to Ca₃Al₂(OH)₁₂ and amorphous aluminum hydroxide. Ca₂Al₂O₅·8H₂O transformed via the intermediate phase Ca₄Al₂O₇·13H₂O to Ca₃Al₂(OH)₁₂ and gibbsite, Al(OH)₃. The phase Ca₄Al₂O₇·19H₂O reacted via the same intermediate phase to Ca₃Al₂(OH)₁₂ and mainly amorphous aluminum hydroxide. The powder pattern of the intermediate phase is reported.     

Synthesis and H2 uptake of Cu2(OH)3Cl, Cu(OH)2 and CuO nanocrystal aggregate

Monodispersed Cu₂(OH)₃Cl nanoplatelets, Cu(OH)₂ nanowires, CuO nanoparticles and nanoribbons with a spherical morphology were synthesized using hydrothermal and heat-treatment reactions, and their H₂ storage characteristics were examined. The Cu₂(OH)₃Cl nanoplatelets particles formed immediately after mixing the reactant, which subsequently formed larger uniform spherical particles in the submicron range. This procedure highlights a practical strategy for producing spherical Cu(OH)₂ and CuO materials consisting of monodispersed nanocrystals. The spherical aggregates of Cu₂(OH)₃Cl nanoplatelets heat-treated at 473 K could reversibly store up to 2.35 wt.% H₂ at 38 bar and 293 K.     

AgBr/Zn3(OH)2V2O7·2H2O可见光催化降解亚甲基蓝溶液

采用水热和沉淀两步合成法制备AgBr/Zn₃(OH)₂V₂O₇·2H₂O催化剂,研究其在可见光下降解亚甲基蓝溶液的性能,并考察催化剂用量、亚甲基蓝溶液初始浓度、pH值以及盐浓度对光催化性能的影响,评价AgBr/Zn₃(OH)₂V₂O₇·2H₂O催化剂的重复使用性能。结果表明,在前驱液pH为10、120 ℃水热10 h、Ag与Br物质的量比为0.20条件下制备的复合催化剂在可见光下反应120 min后,1.0 g·L^-1的催化剂对10 mg·L^-1的亚甲基蓝溶液脱色率达到85.2%。NaCl对亚甲基蓝的降解起抑制作用,Na₂SO₄对亚甲基蓝的降解起促进作用。催化剂重复使用4次后,光照120 min后的亚甲基蓝溶液脱色率可达66.4%。催化剂对不同初始浓度亚甲基蓝溶液的光催化降解符合一级动力学模型。     

Hydrothermal synthesis and characterizations of 2D and 3D 4ZnO·B2O3·H2O nano/microstructures with different morphologies

2D and 3D nano/microstructures of 4ZnO·B₂O₃·H₂O with different morphologies have been successfully synthesized by a hydrothermal route in the presence of surfactant polyethylene glycol-300 (PEG-300). Lamellar-like nanoparticles and microsphere organizations of nano and microrods are fabricated by varying the reaction conditions. The products have been characterized by XRD, FT-IR, TG-DTA and SEM. The XRD data indicate the as-prepared samples present at pure phase 4ZnO·B₂O₃·H₂O with monoclinic symmetry. The SEM results reveal that the lamellar-like particles are about 30 nm in thickness and around several hundred nanometers in diameter. The microsphere organizations have different diameters, and the secondary structures are made from rod-like particles with different size and mode, respectively. The morphologies of products strongly depend on surfactant, hydrothermal temperature and time.     

Hierarchical porous MgBO2(OH) microspheres:Hydrothermal synthesis,thermal decomposition,and application as adsorbents for Congo red removal

A facile eco-friendly hydrothermal route(180 °C, 12.0 h) has been developed for the first time to the uniform hierarchical porous MgBO_2(OH) microspheres without the aid of any organic additive, surfactant or template, by using the abundant MgCl_2·6 H_2 O, H_3BO_3 and NaOH as the raw materials. The as-obtained porous microspheres exhibit a specific surface area of 94.752 mg·g~(-1), pore volume of 0.814 cm3·g~(-1), and ca. 84.0% of which have a diameter of 2.25–3.40 μm. The thermal decomposition of the porous MgBO_2(OH) microspheres(650 °C,2.5 °C·min~(-1)) leads to the porous Mg_2B_2O_5 microspheres with well-retained morphology. When utilized as the adsorbents for the removal of CR from mimic waste water, the present porous MgBO_2(OH) microspheres exhibit satisfactory adsorption capacity, with the maximum adsorption capacity q~(-1) mof 309.1 mg·g, much higher than that derived from most of the referenced adsorbents. This opens a new window for the facile green hydrothermal synthesis of the hierarchical porous MgBO_2(OH) microspheres, and extends the potential application of the 3 D hierarchical porous metal borates as high-efficiency adsorbents for organic dyes removal.     

Two novel isomeric complexes supported by vanadates {V4O12}: [{Cu(dpa)2}2V4O12] (dpa = 2,2′-dipyridylamine)

Two Cu(II) complexes supported by tetravanadates, [{Cu(dpa)₂}₂V₄O₁₂] (1 and 2), have been synthesized under hydrothermal reactions. Structural analysis indicates that complexes 1 and 2 are isomeric and consist of a cyclic [V₄O₁₂]^4- anion bridged to two [Cu(dpa)₂]²⁺ moieties. Close inspection of complexes 1 and 2 reveals that the [V₄O₁₂]^4- anions adopt chair-like and boat-like configurations respectively, and are coordinated to each Cu(II) ions through a single terminal oxygen atom of two cross vanadium sites. Moreover, Complexes 1 and 2 exhibit trans- and cis-configurations, respectively.     

Metal-organic framework Cu3 (BTC)2(H2O)3 catalyzed Aldol synthesis of pyrimidine-chalcone hybrids

A typical metal organic framework, [Cu₃ (BTC)₂(H₂O)₃, BTC = 1,3,5-benzene tricarboxylate] has been used for the synthesis of pyrimidine-chalcones. We have explored a green synthesis of pyrimidine chalcones under Cu₃(BTC)₂ catalysis by Aldol condensation. Easy isolation of product, excellent yield, and recyclable catalyst makes this reaction eco-friendly. The technology was demonstrated to be applicable to the synthesis of a host of chemical hybrids.     

Flame retardant synergism of rubber and Mg(OH)2 in EVA composites

A synergistic effect on flame retardancy was found when acrylonitrile butadiene ultra-fine fully vulcanized powdered rubber (NB-UFPR) was incorporated into ethylene vinyl acetate/nano-magnesium hydroxide (EVA/nano-MH) composite by a new process. The fire performance of EVA and EVA composites was compared in this communication by cone calorimeter test (CCT). The CCT data indicated that the addition of NB-UFPR in EVA/nano-MH system not only reduced the heat release rate, but also prolonged the ignition time of the composite, which is contrary to the effect of NB-UFPR when it was added alone in EVA polymer. Thermogravimetric analysis revealed that nano-MH accelerated the loss of acetic acid, but NB-UFPR assisted to reduce nano-MH's accelerating effect. FTIR spectra showed a new absorption at 3374 cm⁻¹ in the blends of EVA/NB-UFPR and EVA/NB-UFPR/nano-MH.     

Preparation of surface modified nano-Mg(OH)2 via precipitation method

Nano-magnesium hydroxide was prepared via wet precipitation by using the mixture of sodium dodecyl sulfate (SDS) and monoalcohol ether phosphate (MAP) as surface modifiers. The yield of the surface modified nano-Mg(OH)₂ was about 98%. The usage and dosage of surface modifiers were optimized by means of the measurements of suspension volume of the nano-particles in liquid paraffin. As the mass ratio of SDS to MAP was 2:1 and the total of 0.2 wt.% of Mg(OH)₂ theoretical weight (4.35 g) was used, the nano-Mg(OH)₂ with optimized dispersibility was obtained. The volume percent of the surface modified nano-particles suspension in liquid paraffin could reach 96% after 11 h while that of the nano-Mg(OH)₂ without modification would be 62%. The as-prepared samples were characterized through N₂ adsorption, X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry-differential scanning calorimetry (TGA-DSC). The results show that hexagonal crystal nano-particles with both SDS and MAP molecules on the surfaces were obtained. The LOI value of PP composites is 35.0 at 150 phr (50% by weight) of surface modified nano-Mg(OH)₂.     

Photocatalytic degradation of aqueous organocholorine pesticide on the layered double hydroxide pillared by Paratungstate A ion, Mg12Al6(OH)36(W7O24)·4H2O

Layered double hydroxide pillared by Paratungstate A ion, Mg₁₂Al₆(OH)₃₆(W₇O₂₄)·4H₂O, was prepared via anion exchange reaction of the synthetic precursor, Mg₄Al₂(OH)₁₂TA·xH₂O (TA²⁻=terephthalate), and [W₇O₂₄]⁶⁻ ion. Some physico-chemical properties were measured and the preparation conditions were studied. Trace aqueous organocholorine pesticide, hexachlorocyclohexane (HCH), was totally degraded and mineralized into CO₂ and HCl by irradiating a Mg₁₂Al₆(OH)₃₆(W₇O₂₄)·4H₂O suspension in the near UV area. Disappearance of trace HCH follows Langmuir–Hinshelwood first-order kinetics. The model and mechanism for the photocatalytic degradation of HCH on the Mg₁₂Al₆(OH)₃₆(W₇O₂₄)·4H₂O were proposed, indicating that the interlayer space is the reaction field, and that photogeneration of OH√ radicals are responsible for the degradation pathway.     

Carbonate-catalyzed chemiluminescence decomposition of peroxynitrite via (CO2)2 intermediate

Peroxynitrous acid (ONOOH) was formed by the on-line rapid reaction of acidified hydrogen peroxide with nitrite in a simple flow system. A weak chemiluminescent (CL) signal was observed due to the production of singlet oxygen (¹O₂) when ONOOH reacted with NaOH, whereas the replacement of NaOH by Na₂CO₃ markedly enhanced the CL intensity. The predominant CL-enhanced pathway was achieved by the carbonate-catalyzed decomposition of peroxynitrite (ONOO⁻). Carbonate species was regenerated in the process, that is, carbonate acts as a catalyst. Based on the studies of CL and fluorescence spectra, a possible CL mechanism from the reaction of carbonate with ONOOH was proposed. In brief, ONOOH was an unstable compound in acidic solution and could be quenched into ONOO⁻ in basic media. It was suggested that ONOO⁻ reaction with excess HCO₃⁻ proceeded via one-electron transfer to yield bicarbonate ion radicals (HCO₃√). The recombination of HCO₃√ may directly generate excited triplet dimers of two CO₂ molecules [(CO₂)₂^*]. With the decomposition of this unstable intermediate to CO₂, the energy was released by CL emission. The addition of uranine into carbonate solution caused enhancement of the CL signal, which was due to a part of excited triplet dimers of two CO₂ molecules energy to transfer to uranine, resulting in two CL peaks.