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1. Effect of Reaction Time on Phosphate Mineralization from Microalgae Hydrolyzate

   Kumar, S (November 2017, ACS sustainable chemistry & engineering)

   The development of algal biorefineries is strongly associated with the nutrient management, particularly phosphorus, which is a limited mineral resource. Flash hydrolysis (FH) has been widely applied to a variety of algae species to fractionate its constituents. This chemical-free, subcritical water technique was used to extract more than 80 wt % of phosphorus available in the Scenedesmus sp. as water-soluble phosphates in the aqueous phase (hydrolysate). The phosphate-rich hydrolysate was subjected to the hydrothermal mineralization (HTM) process at 280 °C and 5–90 min of residence time to mineralize phosphates as allotropes of calcium phosphate such as hydroxyapatite (HAp) and whitlockite (WH). In the current study, the effect of reaction time on phosphate mineralization from the hydrolysate as well as the composition, structure and the morphology of the precipitates were studied. Calcium hydroxide and commercial HAp were used as the mineralizer and seeding material, respectively. More than 97 wt % of phosphate and almost 94 wt % of calcium were removed in the first 5 min of the HTM process. Results revealed that as the HTM reaction time increased, calcium phosphate precipitates transformed from WH to carbonated HAp. The integration of the proposed mineralization process with FH can be a cost-effective pathway to produce sustainable, and high value phosphate-based bioproducts from algae. The application of HAp includes biomedical applications such as synthetic bone and implant filling, drug delivery, chromatography, corrosion resistance materials, catalytic activities and fertilizers. 

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2. In situ quasi-elastic neutron scattering study on the water dynamics and reaction mechanisms in alkali-activated slags

   https://doi.org/10.1039/c9cp00889f  

   Gong, Kai; Cheng, Yongqiang; Daemen, Luke L.; White, Claire E. (May 2019, Physical Chemistry Chemical Physics)

   null (Ed.)

   In this study, in situ quasi-elastic neutron scattering (QENS) has been employed to probe the water dynamics and reaction mechanisms occurring during the formation of NaOH- and Na 2 SiO 3 -activated slags, an important class of low-CO 2 cements, in conjunction with isothermal conduction calorimetry (ICC), Fourier transform infrared spectroscopy (FTIR) analysis and N 2 sorption measurements. We show that the single ICC reaction peak in the NaOH-activated slag is accompanied with a transformation of free water to bound water (from QENS analysis), which directly signals formation of a sodium-containing aluminum-substituted calcium–silicate–hydrate (C–(N)–A–S–H) gel, as confirmed by FTIR. In contrast, the Na 2 SiO 3 -activated slag sample exhibits two distinct reaction peaks in the ICC data, where the first reaction peak is associated with conversion of constrained water to bound and free water, and the second peak is accompanied by conversion of free water to bound and constrained water (from QENS analysis). The second conversion is attributed to formation of the main reaction product ( i.e. , C–(N)–A–S–H gel) as confirmed by FTIR and N 2 sorption data. Analysis of the QENS, FTIR and N 2 sorption data together with thermodynamic information from the literature explicitly shows that the first reaction peak is associated with the formation of an initial gel (similar to C–(N)–A–S–H gel) that is governed by the Na + ions and silicate species in Na 2 SiO 3 solution and the dissolved Ca/Al species from slag. Hence, this study exemplifies the power of in situ QENS, when combined with laboratory-based characterization techniques, in elucidating the water dynamics and associated chemical mechanisms occurring in complex materials, and has provided important mechanistic insight on the early-age reactions occurring during formation of two alkali-activated slags. 

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3. Calcium phosphate nanocomposites via in situ mineralization in block copolymer hydrogels

   https://doi.org/10.1002/pat.5183  

   Griffin, David M.; Kennedy, Mitchell A.; Bhatia, Surita R. (December 2020, Polymers for Advanced Technologies)

   Significant research has been directed toward producing composites that mimic the micro‐ to nanoscale structure of bone tissue, and it remains a challenge to develop synthetic strategies to create cost‐effective biocomposite materials with nanoscale inorganic domains. In this paper, we report the synthesis of nanocrystalline calcium phosphate minerals in situ in gels of a commercially available block copolymer, Pluronic F127 (F127). Although solutions of F127 have previously been explored as a templating agent for calcium phosphate mineralization, here we demonstrate the synthesis of nano‐sized calcium hydrogen phosphate hydrate directly in F127 gels. Composites formed at pH 7 contained highly crystalline, millimeter‐scale crystals of brushite, while composites created at an initial pH of 11 contained nanoscale particles of a calcium hydrogen phosphate hydrate similar to natural bone apatite in morphology and size, with a mean particle diameter of 120 nm. The in situ composites have storage moduli of 15–25 kPa, which is comparable to mechanically processed hydrogel composites containing four times more inorganic material. We believe that our synthetic strategy may provide a new class of versatile and cost‐effective nanostructured biomaterials for use in understanding and replicating mineralized tissues. 

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4. Exploring mechanochemical reactions at the nanoscale: theory versus experiment

   https://doi.org/10.1039/D3CP00980G  

   Hopper, Nicholas; Sidoroff, François; Rana, Resham; Bavisotto, Robert; Cayer-Barrioz, Juliette; Mazuyer, Denis; Tysoe, Wilfred T. (June 2023, Physical Chemistry Chemical Physics)

   Mechanochemical reaction pathways are conventionally obtained from force-displaced stationary points on the potential energy surface of the reaction. This work tests a postulate that the steepest-descent pathway (SDP) from the transition state to reactants can be reasonably accurately used instead to investigate mechanochemical reaction kinetics. This method is much simpler because the SDP and the associated reactant and transition-state structures can be obtained relatively routinely. Experiment and theory are compared for the normal-stress-induced decomposition of methyl thiolate species on Cu(100). The mechanochemical reaction rate was calculated by compressing the initial- and transition-state structures by a stiff copper counter-slab to obtain the plots of energy versus slab displacement for both structures. The reaction rate was also measured experimentally under compression using a nanomechanochemical reactor comprising an atomic-force-microscopy (AFM) instrument tip compressing a methyl thiolate overlayer on Cu(100) (the same system for which the calculations were carried out). The rate was measured from the indent created on a defect-free region of the methyl thiolate overlayer, which also enabled the contact area to be measured. Knowing the force applied by the AFM tip yields the reaction rate as a function of the contact stress. The result agrees well with the theoretical prediction without the use of adjustable parameters. This confirms that the postulate is correct and will facilitate the calculation of the rates of more complex mechanochemical reactions. An advantage of this approach, in addition to the results agreeing with the experiment, is that it provides insights into the effects that control mechanochemical reactivity that will assist in the targeted design of new mechanochemical syntheses. 

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5. Shear-activated chemisorption and association of cyclic organic molecules

   https://doi.org/10.1039/D2FD00086E  

   Bhuiyan, Fakhrul H.; Li, Yu-Sheng; Kim, Seong H.; Martini, Ashlie (June 2022, Faraday Discussions)

   Mechanochemical activation has created new opportunities for applications such as solvent-free chemical synthesis, polymer processing, and lubrication. However, mechanistic understanding of these processes is still limited because the mechanochemical response of a system is a complex function of many variables, including the direction of applied stress and the chemical features of the reactants in non-equilibrium conditions. Here, we studied shear-activated reactions of simple cyclic organic molecules to isolate the effect of chemical structure on reaction yield and pathway. Reactive molecular dynamics simulations were used to model methylcyclopentane, cyclohexane, and cyclohexene subject to pressure and shear stress between silica surfaces. Cyclohexene was found to be more susceptible to mechanochemical activation of oxidative chemisorption and subsequent oligomerization reactions than either methylcyclopentane or cyclohexane. The oligomerization trend was consistent with shear-driven polymerization yield measured in ball-on-flat sliding experiments. Analysis of the simulations showed the distribution of carbon atom sites at which oxidative chemisorption occurred and identified the double bond in cyclohexene as being the origin of its shear susceptibility. Lastly, the most common reaction pathways for association were identified, providing insight into how the chemical structures of the precursor molecules determined their response to mechanochemical activation. 

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