a b s t r a c tA mesoporous material, titanate nanotubes (TNs) with different surface areas (197-312 m 2 g À1 ) and pore size diameters (2-6 nm) was synthesized by alkaline hydrothermal method. Their adsorption abilities to arsenic, the notoriously poisonous inorganic contaminant in groundwater were evaluated. Batch experiments showed that the adsorption of arsenate [As (V)] was more favored in acid solution, while the uptake of arsenite [As (III)] was preferred in alkaline solution. The maximum uptake of As (V) and As (III) calculated by Langmuir equation was 208 mg g À1 (pH 3.0) and 60 mg g À1 (pH 7.0) respectively achieved on TN (180-1) adsorbent (312 m 2 g À1 , internal diameter, 5 nm), which was 33 and 10 times greater than those of nanosized titania particles (40-50 nm, 15 mg g À1 ). Silicate anions, phosphate and sulfate had little effect on arsenic adsorption onto TNs. In several real water samples, TNs still showed high uptake efficiency to arsenic at pH 7.0. More than 80% of As (III) and 95% of As (V) adsorbed on TNs could be desorbed with 1.0 M NaOH solution within 1 h. Comparison study indicated that all the tubular titanate materials exhibited great adsorption capacity to arsenic regardless their surface areas. Since the equipment required for TNs synthesis is simple and cheap, and alkali solutions are reusable, TNs can be regarded as an efficient, low-cost adsorbent for the removal of arsenic.

The perovskite (Pv) SrIrO 3 is an exotic narrow-band metal owing to a confluence of the strengths of the spin-orbit coupling (SOC) and the electron-electron correlations. It has been proposed that topological and magnetic insulating phases can be achieved by tuning the SOC, Hubbard interactions, and/or lattice symmetry. Here, we report that the substitution of nonmagnetic, isovalent Sn 4+ for Ir 4+ in the SrIr 1-x Sn x O 3 perovskites synthesized under high pressure leads to a metal-insulator transition to an antiferromagnetic phase at T N ≥ 225 K. The continuous change of the cell volume as detected by X-ray diffraction and the λ-shape transition of the specific heat oncooling through T N demonstrate that the metal-insulator transition is of second-order. Neutron powder diffraction results indicate that the Sn substitution enlarges an octahedral-site distortion that reduces the SOC relative to the spin-spin exchange interaction and results in the type-G AF spin ordering below T N . Measurement of high-temperature magnetic susceptibility shows the evolution of magnetic coupling in the paramagnetic phase typical of weak itinerant-electron magnetism in the Sn-substituted samples. A reduced structural symmetry in the magnetically ordered phase leads to an electron gap opening at the Brillouin zone boundary below T N in the same way as proposed by Slater. 17, 18However, the temperature dependence of thermoelectric power does not follow the Mott diffusive formula for a metal. An enhancement of |S| that peaks at ~175 K cannot be rationalized by the phonon-drag effect, which should occur at a small fraction of the Debye temperature. 33The resistivity shows an anomaly at approximately the same temperature. In metallic PV SrRhO 3where the SOC effect is relatively weak, an enhancement near 180 K can still be discerned in S(T), but the enhancement is much smaller than that found in SrIrO 3 . This comparison highlights the possible SOC effect on the thermoelectric power, which deserves a further study. Introducing Back to the case of SrIr 1-x Sn x O 3 , the origin of the magnetism in the Sn-substituted samples is rooted in the parent oxide SrIrO 3 although it is a paramagnetic metal. The EEC effect can be probed through the ratio of γ/γ 0 , where γ is the Sommerfeld coefficient of the specific heat (see Fig. S3 and Table S1 for details) and γ 0 is the calculated electronic contribution from the band structure. 21 For SrIrO 3 , a ratio γ/γ 0 ≈ 1.1 indicates a modest correlation enhancement. However, the ratio of the temperature-independent term χ 0 obtained from the magnetic susceptibility of Determining how the Sn 4+ substitution in SrIr 1-x Sn x O 3 further enhances the interatomic magnetic coupling so as to eventually trigger the magnetic transition relies on our understanding of (1) the substitution effect on the crystal structure and (2) the explicit role of SOC on the spin-spin exchange interaction. Depending on the strength of SOC, the electronic state can be governed by either the crystal field splitting o...

We report on the high-pressure syntheses and detailed characterizations of two effective pseudospin S-1/2 XY pyrochlores Er 2 Pt 2 O 7 andYb 2 Pt 2 O 7 via X-ray/neutron powder diffraction, dc and ac magnetic susceptibility, and specific-heat measurements down to 70 mK. We found that both compounds undergo long-range magnetic transition at T N,C ≈ 0.3 K, which are ascribed to an antiferromagnetic-and ferromagnetic-type order for Er 2 Pt 2 O 7 and Yb 2 Pt 2 O 7 , respectively, based on the field dependence of their transition temperature as well as the systematic comparisons with other similar pyrochlores R 2 B 2 O 7 (R = Er, Yb; B = Sn, Ti, Ge). The observed T N of Er 2 Pt 2 O 7 is much lower than that expected from the relationship of T N versus the ionic radius of B 4+ derived from the series of Er 2 B 2 O 7 , while the T C of Yb 2 Pt 2 O 7 is the highest among the series of ferromagnetic Yb 2 B 2 O 7 (B = Sn, Pt, Ti). Given the monotonic variation of the lattice constant as a function of the B-cation size across these two series of R 2 B 2 O 7 (R = Er, Yb), the observed anomalous values of T N,C in the Pt-based XY pyrochlores imply another important factor beyond the nearest-neighbor R-R distance is playing a role. In light of the anisotropic exchange interactions J ex = {J zz , J ± , J ±± , J z± } for the S-1/2 XY pyrochlores, we have rationalized these observations by considering a weakened (enhanced) antiferromagnetic planar J ± (ferromagnetic Ising-like J zz ) due to strong Pt 5d-O 2p hybridization within the plane perpendicular to the local [111] direction.