Hang Ping

Template-free synthesis of hierarchical porous calcium carbonate microspheres for efficient water treatment

A uniform, hierarchical porous vaterite calcium carbonate microsphere stacked from nanoparticles is synthesized in dimethylformamide–water (DMF–H2O) mixed solvent without template. We propose a solvent-reaction assisted synthesis of the product by a mesoscale growth pathway. The product shows large removal capacity towards Pb2+, Cd2+ and Zn2+, of 1960 mg g−1, 1040 mg g−1 and 587.3 mg g−1, respectively. It also exhibits efficient and selective adsorption of Congo red (272 mg g−1, 5 min for equilibrium), which is reported for the first time on calcium carbonate. The removal mechanism is demonstrated to be the precipitation transformation for the heavy metal ion sequestration, and adsorption mechanism for the removal of the organic dyes. The good performance of the product is ascribed to the large amount of active adsorption sites provided by the nanoscale building blocks and mesopores, and the short pathway provided by the sunken poles and the hierarchical structure with enhanced mass transfer and decreased blocking of channels.

Organized intrafibrillar mineralization, directed by a rationally designed multi-functional protein

Taking lessons from the structure-forming process of biominerals in animals and plants, one can find tremendous inspirations and ideas for developing advanced synthesis techniques, which is called bio-process inspired synthesis. Bone, as a typical representative of biominerals, is constituted of mineralized collagen fibrils, which are formed under the functions of non-collagenous proteins (NCPs). Intrafibrillar mineralization is the consequence of a synergy among several NCPs. In the present study, we have designed a multi-functional protein, named (MBP)-BSP-HAP, based on bone sialoprotein (BSP) and hydroxyapatite binding protein (HAP), to mimic the intrafibrillar mineralization process in vitro. The three functional domains of (MBP)-BSP-HAP provide the artificial protein with multiple designated functions for intrafibrillar mineralization including binding calcium ions, binding collagen, and binding hydroxyapatite. Platelet-like hydroxyapatite crystals periodically arranged inside the collagen fibrils have been achieved under the function of (MBP)-BSP-HAP. The mechanism of intrafibrillar mineralization directed by the multi-functional protein was proposed. This work may not only shed light on bio-process inspired approaches for more economic and efficient biomimetic synthesis, but also be helpful in understanding the natural process of bone formation for bone regeneration and tissue repair.

Photo-assisted synthesis of Au@PtAu core–shell nanoparticles with controllable surface composition for methanol electro-oxidation

Surface composition control plays a crucial role in electrocatalytic reactions for Pt-based bimetallic materials. However, strategies for controlling their surface composition always require extreme conditions including the use of harsh agents, the need for high temperatures, and the necessity of complex procedures. Here we develop a photo-assisted method to fabricate Au@PtAu core–shell nanoparticles (NPs) with well-tuned surface composition at ambient temperatures. It was found that their surface composition can be continuously regulated by the addition amount of HAuCl4 under photo-irradiation. By incorporating Au atoms, the synthesized Au@PtAu NPs show significantly improved properties for methanol electro-oxidation, owing to the reduced CO formation and the weakened binding strength of CO on Pt. The catalytic activity and durability vary with the relative active surface area of Pt or Au (PtSurf. or AuSurf.), and the optimal PtSurf. was found to be ∼64% (AuSurf. ∼36%). The present work highlights the “photo-assisted method” as a green and effective method to synthesize advanced materials with optimized functional properties.

Confinement controlled mineralization of calcium carbonate within collagen fibrils

Confinement is common in biological systems and plays a critical role in the structure-forming process of biominerals. However, the knowledge of confinement effects on biomineralization is limited due to the lack of specific chemical structures and elaborate spatial distribution. In this article, we explore the confined mineralization of amorphous calcium carbonate (ACC) within collagen fibrils. Three issues of the confined mineralization of ACC within collagen fibrils were investigated, including the morphology and characteristics of the confined mineralization of ACC within collagen fibrils; the initiation and development of the confined mineralization of ACC within collagen fibrils; and the driving mechanism of ACC infiltration into collagen fibrils. Results show that the negatively charged ACC droplets were attracted to positively charged gap regions of collagen fibrils through electrostatic interactions, infiltrated into collagen fibrils, and then transformed into the crystalline phase. The observation of juxtaposed crystalline and amorphous phases on the surface of fibrils indicates that a secondary nucleation mechanism may be responsible for the co-orientation of calcite nanocrystals. Through modifying the wettability of amorphous calcium carbonate with magnesium ions, it is verified that the infiltration of ACC into collagen fibrils was driven by capillary forces. The present study not only provides evidence of the confinement effects in biomineralization but also facilitates the understanding of the in vivo bone formation process. It may also open up a new avenue in the bioprocess-inspired synthesis of advanced materials.

A bio-process inspired synthesis of vaterite (CaCO3), directed by a rationally designed multifunctional protein, ChiCaSifi

Living organisms can produce elegant structures with unique functions and properties through biological processes. Various proteins are involved in these processes. Inspired by the structure formation of mollusc shells, a single multifunctional recombinant protein ChiCaSifi was designed on the basis of mineralization proteins for regulating CaCO3 mineralization in a simple and direct manner. ChiCaSifi contains functional domains of the chitin binding protein (Chi), the calcium binding protein (Ca), and the silk fibroin (Sifi). Therefore, ChiCaSifi can have multiple roles in directing CaCO3 mineralization. Overexpression and purification of ChiCaSifi were achieved. Activities of ChiCaSifi were examined for its binding to calcium and chitin. Influences of ChiCaSifi in regulating the phase formation of CaCO3 crystals on the chitin surface were proved. Structural changes of ChiCaSifi were evidenced and related to its functions on mineralization. These observations indicate that rationally designed proteins with functional domains of mineralization proteins can be effective tools in materials synthesis. The present study may not only provide an insight into the formation of natural biomaterials, but also open a new avenue in the design and synthesis of novel organic-inorganic composite materials.

Crystallization of calcium carbonate under the influences of casein and magnesium ions

Various proteins and molecules are involved in the crystallization pathways of biomineralization. The present study investigated the involvement of casein and magnesium ions in the crystallization of calcium carbonate (CaCO3). The calcium carbonate crystals obtained under the control of casein and magnesium ions were characterized by various techniques such as XRD and FTIR. Results showed that the morphology of the CaCO3 crystals was significantly affected by casein and magnesium ions. The secondary structure of casein proteins and the size of casein micelles play important roles in the morphological construction of CaCO3 crystals. Magnesium ions can directly interact with CaCO3 crystals to affect the morphology. Magnesium ions are also indirectly involved in the casein assisted CaCO3 mineralization by affecting the size of casein micelles to regulate the CaCO3 mineralization. This work may not only provide insight into natural biomineralization process, but also be helpful in designing and synthesizing novel functional materials.

Controlled synthesis of mesoporous nanostructured anatase TiO2 on a genetically modified Escherichia coli surface for high reversible capacity and long-life lithium-ion batteries

TiO2 is a promising anode material for lithium-ion batteries. The electrochemical performance of TiO2 can be improved by optimization of nanostructures. The present study was proposed to control the synthesis of mesoporous nanostructured anatase TiO2 on a genetically modified Escherichia coli surface. A recombinant protein INP-SiliSila containing functional domains of silicatein-α and silaffin was constructed and expressed on the E. coli surface. Deposition of the TiO2 precursor was facilitated by INP-SiliSila on the E. coli surface. Upon calcination, TiO2 coating on the E. coli surface transformed to anatase and formed well-defined rod-shaped particles. The electrochemical performance of the as-prepared anatase TiO2 as anode electrodes was improved and better than that of most reported ones. The present study not only provides an organism-based approach for fabricating nanostructured anatase TiO2 with enhanced electrochemical performance, but also opens a new avenue to take advantage of genetically modified bacterial surfaces in the synthesis and structure control of materials.

Induced transformation of amorphous silica to cristobalite on bacterial surfaces

Extreme conditions such as high temperature and/or pressure are usually required for the transformation of amorphous silica to crystalline polymorphs. In this article, we present our results that amorphous silica can be deposited on a bacterial surface and transformed to cristobalite at a relatively low temperature and ambient pressure. The phase transformation of amorphous silica to cristobalite under thermal treatment was investigated by a variety of methods including X-ray diffraction, electron microscopy, and Fourier transform infrared spectroscopy. Results show that amorphous silica on a bacterial cell surface exhibits a direct phase transformation to cristobalite structure at a relatively low temperature (800 °C). The surface charge of the bacterial cells does not affect the phase transformation. Three Gram-negative bacteria and three Gram-positive bacteria have been tested in the present study. All these bacteria have been found to facilitate the phase transition of amorphous silica into cristobalite. The observation of amorphous silica transformation on bacterial surfaces to cristobalite highlights the use of bacteria in the synthesis and structure control of silica minerals.

Sol-gel Autocombustion Synthesis of Nanocrystalline High-entropy Alloys

A reduction in the particle size is expected to improve the properties and increase the application potential of high-entropy alloys. Therefore, in this study, a novel sol–gel autocombustion technique was first used to synthesize high-entropy alloys. The average grain size of the prepared nanocrystalline CoCrCuNiAl high-entropy alloys showed was 14 nm with an excellent and uniform dispersion, exhibiting a distinct magnetic behavior similar to the superparamagnetic behavior. We show that the metal nitrates first form (Co,Cu,Mg,Ni,Zn)O high-entropy oxides, and then in situ reduce to CoCrCuNiAl high-entropy alloys by the reducing gases, and the chelation between citric acid and the metal ions and the in situ chemical reactions are the dominant reaction mechanisms. We demonstrate that the sol–gel autocombustion process is an efficient way to synthesize solid solution alloys eluding the restriction of a high mixing entropy.

One-pot synthesis of bio-inspired layered materials of 3D graphene network/calcium carbonate

A bio-inspired layered material of reduced graphene oxide (RGOs) and calcium carbonate was synthesized via a one-pot strategy in DMF/H2O mixed solvent. The experimental results show that the product is a layered material of wrinkled RGOs networks and micron-sized calcium carbonate particles with uniform granular diameter and homogeneous morphology, which are distributed between the layered gallery of the graphene scaffold. The polymorph and the morphology of the in-situ produced calcium carbonate particles can be manipulated by simply changing the temperature scheme. Besides, the graphene oxide was reduced to a certain extent, and the hierarchical wrinkles were generated in the RGOs layer by the in-situ formation of the calcium carbonate particles. This work provides a facile and controllable strategy for synthesizing layered material of RGOs and carbonates, and also presents a platform for making three-dimensional porous wrinkled RGOs networks.