Mingyang Zhao,Xiao Chen,Huiping Zhu,Songqin Xia,Yan Ma,Kyle S. Brinkman,Zhenfeng Tong
This study systematically explored the crystal chemistry of Fe-substituted hollandite (Fe-hollandite) solid solutions (Ba x Cs y )(Fe 2 x + y Ti 8−2 x − y )O 16 ( x + y = 1.33) yielding reliable results through meticulous Rietveld analysis of XRD data. Continuous Cs substitution triggered a monoclinic-tetragonal (M-T) phase transition, enhancing structural stability, as evidenced by increased tolerance factor ( t H ). The transition boundary, controlled by t H = .985, determines the symmetry of the hollandite phase. Unit cell parameters and the local bonding environment were refined, indicating enlarged tunnel sizes/cavities with higher Cs content, attributed to a larger ionic radius (Cs + vs. Ba 2+ ). Comparison between Cs/Ba-O bond distances and tunnel cross-section sizes confirmed effective A-site cation immobilization, hindered by oxygen bottlenecks. Additionally, a refined model was proposed and validated to predict lattice constants of Fe-hollandite precisely. Beyond crystal chemistry evolution with Cs substitution, leaching resistance in the same sample suites was assessed. As Cs content increased, normalized elemental release of A-site cations initially decreased until reaching a minimum at intermediate Cs substitution, then rose again. Ba 0.33 Cs 1.0 Fe 1.66 Ti 6.34 O 16 (i.e., HF5) displayed optimal leaching resistance. Variations in leaching resistance might be influenced by the distortion in [BO 6 ] octahedra and the bonding environment of tunnel cations. This comprehensive analysis highlights intricate correlations between crystal chemistry and leaching resistance, offering insights to guide the design of advanced crystalline nuclear waste forms with enhanced corrosion resistance.
In this study, a new method was developed for the oxidation of 5-hydroxymethylfurfural (HMF) into 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) over heterogeneous Ru catalyst. Cs-substituted tungstophosphate (CsPW) was prepared by the exchange of H + in H 3 PW 12 O 40 with Cs + , which was then used to immobilize Ru nanoparticles to give the Ru/CsPW catalyst. The Ru/CsPW catalyst was well characterized by TEM, XRD, XPS and FT-IR technologies. The physical characterizations clearly indicated that the spherica Ru nanoparticles with an average size of 2.4 nm were homogeneously dispersed on the surface of the CsPW support. The as-prepared catalyst was studied for the oxidation of HMF, and some important parameters were investigated. The reaction solvent showed a great effect on both HMF conversion and the products selectivity. Aromatic solvents were found to be the best reaction medium for the oxidation of HMF into HMFCA. Increasing the reaction temperature and the amount of the Ru/CsPW catalyst accelerated the HMF conversion and HMFCA yield. High HMF conversion of 97.2% and HMFCA yield of 72.9% were obtained after 12 h at 130 °C with oxygen flow rate of 20 ml/min. Unfortunately, the Ru/CsPW catalyst was not very stable during the reaction, and a slight loss of its catalytic activity was observed during the recycling experiments.
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