Baozhong Liu

Unique Lead Adsorption Behavior of Activated Hydroxyl Group in Two-Dimensional Titanium Carbide

The functional groups and site interactions on the surfaces of two-dimensional (2D) layered titanium carbide can be tailored to attain some extraordinary physical properties. Herein a 2D alk-MXene (Ti3C2(OH/ONa)(x)F(2-x)) material, prepared by chemical exfoliation followed by alkalization intercalation, exhibits preferential Pb(II) sorption behavior when competing cations (Ca(II)/Mg(II)) coexisted at high levels. Kinetic tests show that the sorption equilibrium is achieved in as short a time as 120 s. Attractively, the alk-MXene presents efficient Pb(II) uptake performance with the applied sorption capacities of 4500 kg water per alk-MXene, and the effluent Pb(II) contents are below the drinking water standard recommended by the World Health Organization (10 μg/L). Experimental and computational studies suggest that the sorption behavior is related to the hydroxyl groups in activated Ti sites, where Pb(II) ion exchange is facilitated by the formation of a hexagonal potential trap.

Synthesis of MXene/Ag Composites for Extraordinary Long Cycle Lifetime Lithium Storage at High Rates

A new MXene/Ag composite was synthesized by direct reduction of a AgNO3 aqueous solution in the presence of MXene (Ti3C2(OH)0.8F1.2). The as-received MXene/Ag composite can be deemed as an excellent anode material for lithium-ion batteries, exhibiting an extraordinary long cycle lifetime with a large capacity at high charge-discharge rates. The results show that Ag self-reduction in MXene solution is related to the existence of low-valence Ti. Reversible capacities of 310 mAh·g(-1) at 1 C (theoretical value being ∼320 mAh·g(-1)), 260 mAh·g(-1) at 10 C, and 150 mAh·g(-1) at 50 C were achieved. Remarkably, the composite withstands more than 5000 cycles without capacity decay at 1-50 C. The main reasons for the long cycle life with high capacity are relevant to the reduced interface resistance and the occurrence of Ti(II) to Ti(III) during the cycle process.

Degradation behavior of Mg-based biomaterials containing different long-period stacking ordered phases

Long-period stacking ordered (LPSO) phases play an essential role in the development of magnesium alloys because they have a direct effect on mechanical and corrosion properties of the alloys. The LPSO structures are mostly divided to 18R and 14H. However, to date there are no consistent opinions about their degradation properties although both of them can improve mechanical properties. Herein we have successfully obtained two LPSO phases separately in the same Mg-Dy-Zn system and comparatively investigated the effect of different LPSO phases on degradation behavior in 0.9 wt.% NaCl solution. Our results demonstrate that a fine metastable 14H-LPSO phase in grain interior is more effective to improve corrosion resistance due to the presence of a homogeneous oxidation film and rapid film remediation ability. The outstanding corrosion resistant Mg-Dy-Zn based alloys with a metastable 14H-LPSO phase, coupled with low toxicity of alloying elements, are highly desirable in the design of novel Mg-based biomaterials, opening up a new avenue in the area of bio-Mg.

Synthesis of urchin-like rutile titania carbon nanocomposites by iron-facilitated phase transformation of MXene for environmental remediation

Self-assembling has been confirmed as an effective pathway to achieve some unique properties. The recently developed two-dimensional transition metal carbides (termed MXene) provide more potential opportunities to modify the surfaces of layered materials relative to simple graphene. Here we describe a one-step method for preparing an urchin-like rutile TiO2–C (u-RTC) nano-composite with a high amount of (110) facets by in situ phase transformation of MXene (Ti3C2(OH)0.8F1.2) under FeCl3 conditions. A layered anatase TiO2–C (l-ATC) nano-composite with a high percentage of (001) facets first forms, and then it changes into u-RTC due to the Fe(III) ion induction. The u-RTC displays a high Cr(VI) adsorption capacity of ∼225 mg g−1, which is higher than that of the primitive MXene (∼62 mg g−1) and the l-ATC precursor (∼11 mg g−1), owing to the inhibition of H2O molecule adsorption by bridging oxo groups in terms of the first principles calculations. Apart from the fact that the finding leads to a desirable aligned oxide-carbon material, this approach may set up a new trajectory to self-assemble functional surfaces of other MXene derivatives.

Synthesis of Nanoflower-Shaped MXene Derivative with Unexpected Catalytic Activity for Dehydrogenation of Sodium Alanates

Surface group modification and functionalization of two-dimensional materials in many cases are deemed as effective approaches to achieve some distinctive properties. Herein, we present a new nanoflower-shaped TiO2/C composite which was synthesized by in situ alcoholysis of two-dimensional layered MXene (Ti3C2(OHxF1-x)2) in a dilute HF solution (0.5 wt %) for the first time. Furthermore, it is demonstrated that it bestows a strong catalytic activity for the dehydrogenation of NaAlH4. The results show that the NaAlH4 containing 10 wt % A0.9R0.1-TiO2/C (containing 90% anatase TiO2 and 10% rutile TiO2) composite merely took ∼85 min to reach a stable and maximum dehydrogenation capacity of ∼3.08 wt % at 100 °C, and it maintains stable after ten cycles, which is the best Ti-based catalyst for the dehydrogenation of NaAlH4 reported so far. Theoretical calculation confirms that this C-doping TiO2 crystals remarkably decreases desorption energy barrier of Al-H bonding in NaAlH4, accelerating the breakdown of Al-H bonding. This finding raises the potential for development and application of new fuel cells.

Investigations on hydrogen storage properties of LaMg8.52Ni2.23M0.15 (M=Ni, Cu, Cr) alloys

Abstract LaMg 8.52 Ni 2.23 M 0.15 (M=Ni, Cu, Cr) alloys were prepared by induction melting. X-ray diffraction showed that all the three alloys had a multiphase structure, consisting of La 2 Mg 17 , LaMg 2 Ni and Mg 2 Ni phases. Energy dispersive X-ray spectrometer results revealed that most of Cu and Cr distributed in Mg 2 Ni phase. La 2 Mg 17 and LaMg 2 Ni phases decomposed into MgH 2 , Mg 2 NiH 4 and LaH 3 phases during the hydrogenation process. Hydriding/dehydriding measurements indicated that the reversible hydrogen storage capacities of Mg 2 Ni phase in LaMg 8.52 Ni 2.23 M 0.15 (M=Cu, Cr) alloys increased to 1.05 wt.% and 0.97 wt.% from 0.79 wt.% of Mg 2 Ni phase in LaMg 8.52 Ni 2.38 alloy at 523 K. Partial substitution of Cu and Cr for Ni decreased the onset dehydrogenation temperature of the alloy hydrides and the temperature lowered by 18.20 and 5.50 K, respectively. The improvement in the dehydrogenation property of the alloys was attributed to that Cu and Cr decreased the stability of Mg 2 NiH 4 phase.

Effect of lanthanum hydride on microstructures and hydrogen storage performances of 2LiNH2-MgH2 system

Abstract Hydrogen storage properties of 2LiNH 2 -MgH 2 system were improved by adding lanthanum hydride (LaH 3 ), and the role of LaH 3 in hydrogen sorption process of Li-Mg-N-H system was investigated. Temperature programmed sorption results showed that the addition of lanthanum hydride reduced the dehydriding/hydriding onset temperature of 2LiNH 2 -MgH 2 system by at least 15 K. Moreover, A 0.053 wt.%/min average rate was determined for the hydrogen desorption of 2LiNH 2 -MgH 2 -0.05LaH 3 composite, while it was only 0.035 wt.%/min for 2LiNH 2 -MgH 2 system. Hydrogen absorption capacity increased from 1.62 wt.% to 2.12 wt.% within 200 min by adding LaH 3 into 2LiNH 2 -MgH 2 system at 383 K. In the dehydrogenation of 2LiNH 2 -MgH 2 -0.05LaH 3 composite, LaH 2 transferred to LaN phase, which reversed to LaH 2 in the following hydrogen adsorption process. The reversible reaction of LaH 2 effectively promoted the hydrogen sorption of Li-Mg-N-H system. Moreover, the homogenous distribution of fine La hydride was favorable to improving effect of lanthanum hydride.

Phase structure and hydrogen storage properties of REMg8.35Ni2.18Al0.21 (RE=La, Ce, Pr, and Nd) hydrogen storage alloys

REMg8.35Ni2.18Al0.21 (RE=La, Ce, Pr, and Nd) alloys were prepared by induction melting and following annealing. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the alloys were composed of Mg2Ni, (La, Pr, Nd)Mg2Ni, (La, Ce)2Mg17, (Ce, Pr, Nd)Mg12 and Ce2Ni7 phases. The above phases were disproportioned into Mg2NiH4, MgH2 and REHx (x=2.51 or 3) phases in hydriding. CeH2.51 phase transformed into CeH2.29 phase in dehydriding, whereas LaH3, PrH3 and NdH3 phases remained unchanged. The PrMg8.41Ni2.14Al0.20 alloy had the fastest hydriding kinetics and the highest dehydriding plateau pressure while the CeMg8.35Ni2.18Al0.21 alloy presented the best hydriding/dehydriding reversibility. The onset hydrogen desorption temperature of the CeMg8.35Ni2.18Al0.21 hydride decreased remarkably owing to the phase transformation between the CeH2.51 and the CeH2.29.

Hydrogen absorption–desorption characteristics of a Gd2Co7-type Sm1.6Mg0.4Ni7 compound

In this paper, we report a new Gd2Co7-type Sm1.6Mg0.4Ni7 compound as a hydrogen storage material with a special hydrogen absorption/desorption process and good hydrogen storage ability. The Gd2Co7-type Sm1.6Mg0.4Ni7 compound absorbs 1.88 wt% H2 within 17 min at 298 K under 10 MPa H2. Meanwhile, the hydrogen absorption speed accelerates to 3.4 min after 20 hydrogenation/dehydrogenation cycles with a 1.44 wt% H2 under 3 MPa H2. Especially, the capacity retention of the compound is 99.3% at the 100th cycle. We found the hydrogen absorption/desorption of the compound undergoes two equilibrium stages, relating to the transformation of H2 between H-solid solution phase and hydride phase with a lower rate and higher enthalpy change at the lower concentration H2 stage, and the direct conversion between H2 and the hydride phase with a higher rate and lower enthalpy change at the higher concentration H2 stage. The two step mode lowers the inner-molecular strain and mismatch in subunit volumes of the compound in hydrogen absorption/desorption, caused by the transformation of H2 at the lower concentration of H2 stage, thus leading to good structural stability and excellent cycling stability. The new insights are expected to provide viable intermetallic materials as high-pressure tank materials for hydrogen storage with nice hydrogen storage properties.