RSC Advances

Aadhavan, R.; Babu, K. Suresh

doi: 10.1039/c5ra12278cpmid: N/A

Cerium oxide based nanostructure coatings are shown to be promising for high temperature oxidation protection of AISI 304 stainless steel due to the presence of oxygen vacancy defects. The present work focuses on the correlation of oxygen vacancies generated by varying lanthanum concentration in ceria to high temperature oxidation protection. LaxCe1−xO2−δ (x = 0, 0.05, 0.1, 0.2 & 0.4) synthesized using a chemical co-precipitation method was sintered at 1473 K for 5 hours and used as a target in electron-beam physical vapour deposition (EBPVD). The thickness of the coatings over the AISI 304 substrate was maintained at 2000 nm and all the samples were isothermally oxidized at 1243 K for 24 hours. The La3+ doping and the presence of oxygen vacancies were confirmed by using X-ray diffraction and Raman spectroscopy, respectively, in the as coated condition. Though the target had larger mean crystallite size (77 to 52 nm) but varied marginally (6.7 to 7.3 nm) in the as coated condition emphasizing the role of physical process during deposition. The rate constant value for the oxidation process was found to be 3–4 orders lower than that of bare AISI 304 indicating the effect of coating against high temperature oxidation. 5% La doped ceria coating provided better oxidation protection than pure ceria while 40% doping resulted in one order lower rate. This can be attributed to the higher oxygen vacancy concentration present in the sample. The presence of La in the coatings also helped in the retention of oxygen vacancy concentration after oxidation. The reported study indicates the importance of oxygen vacancy tuning and need for uniform coatings towards designing coatings for high temperature oxidation protection.

Sivaraman, P.; Mishra, Sarada P.; Potphode, Darshna D.; Thakur, Avinash P.; Shashidhara, K.; Samui, Asit B.; Bhattacharyya, Arup R.

doi: 10.1039/c5ra13136gpmid: N/A

Multi-walled carbon nanotubes (MWCNTs) were partially unzipped longitudinally by a chemical method. Unzipped multi-walled carbon nanotubes (UZ-MWCNTs) were characterized by transmission electron microscopic analysis, X-ray diffraction and Raman spectroscopic analyses. UZ-MWCNTs were utilized for electrode preparation and the electrodes were used in the fabrication of a supercapacitor. At room temperature, the UZ-MWCNTs based supercapacitor showed a specific capacitance of ∼41 F g−1, while pristine MWCNTs based supercapacitor exhibited 22 F g−1 at the scan rate of 25 mV s−1. The increase in specific capacitance was attributed to an increase in effective specific surface area of UZ-MWCNTs due to partial unzipping. UZ-MWCNTs based supercapacitor exhibited an increase in specific capacitance with increase in temperature. It showed a specific capacitance of ∼74 F g−1 at 100 °C at the scan rate of 25 mV s−1, while the pristine MWCNTs based supercapacitor did not show any appreciable change in specific capacitance as a function of temperature. UZ-MWCNTs exhibited three-fold increase in specific capacitance as compared to pristine MWCNTs at 100 °C. Impedance spectroscopic analysis of the supercapacitors revealed that the UZ-MWCNTs based supercapacitor exhibited higher internal resistance and lower leakage resistance than pristine MWCNTs based supercapacitor. Continuous ‘charge–discharge’ cycling behaviour indicated that the UZ-MWCNTs based supercapacitor exhibited less stability during initial cycles even though it depicted higher specific capacitance as compared to the pristine MWCNTs based supercapacitor.

Ladenhauf, Eva M.; Pum, Dietmar; Wastl, Daniel S.; Toca-Herrera, Jose Luis; Phan, Nam V. H.; Lieberzeit, Peter A.; Sleytr, Uwe B.

doi: 10.1039/c5ra14971apmid: N/A

This work describes the development of molecularly imprinted polymer (MIP) thin films by using reassembled S-layer protein arrays as templates. Crystalline bacterial cell surface layer (S-layer) proteins are among the most abundant biopolymers on earth and form the outermost cell envelope component in a broad range of bacteria and archaea. The unique feature of S-layer based imprints is the crystalline character of the reassembled S-layer protein lattice leading to a precisely controllable periodicity of surface functional groups and topographical features. By determining the Young (elastic) modulus of the S-layer protein with respect to that of the polymer at its gel point, the feasibility of the S-layer based biomolecular imprinting was confirmed. After imprinting the polymer with an S-layer coated silicon stamp, the sensitivity of the imprints and their selectivity in relation to various other proteins were investigated by quartz crystal microbalance (QCM) studies. Furtheron, polycationic ferritin (PCF) was bound in a dense packing on the S-layer and subsequently used for stamping. Successful rebinding of PCF proved that the S-layer lattice can be used as a template for making imprints of densely packed and, probably, perfectly oriented biologically functional molecules, a concept that can in principle be extended to a wide range of other biomolecules (e.g. antibodies).

Banerjee, Rakesh; Parida, Sheetal; Maiti, Chiranjit; Mandal, Mahitosh; Dhara, Dibakar

doi: 10.1039/c5ra17158jpmid: N/A

Controlled and efficient delivery of therapeutics to tumor cells is one of the key issues in cancer therapy. In the present work, a new class of water soluble core cross-linked polymer nanoparticles (CLPNs) possessing acid degradable core and thermoresponsive shell was synthesized for pH-triggered delivery of drugs to cancerous cells. The diol groups of the poly(ethylene glycol)-b-poly(N-isopropylacrylamide)-b-poly(glycidyl methacrylate) diol triblock copolymer were utilized to form the core cross-linked polymeric nanoparticles through an arm-first method by reaction with aldehyde functionalized cross-linkers through formation of acetal linkages. The encapsulation efficiency as well as the release properties of these CLPNs was investigated using doxorubicin (DOX), a known anticancer drug. The release was found to be preferable at the desired lysosomal pH (∼5.0) of the cancer cells and below the LCST (∼32 °C) of poly(N-isopropylacrylamide) (PNIPA). The cytotoxicities of the precursor polymer as well as the CLPNs were tested on the growth of NIH/3T3, normal mouse fibroblast cells, and they were found to be nontoxic. The anticancer activity of the DOX loaded CLPN was confirmed using cervical cancer cell lines HeLa and SiHa by MTT assay, morphological studies and flow cytometry. These studies revealed an increased accumulation of the drug around the nucleus when treated with DOX-loaded CLPN as compared to free DOX along with significant reduction in IC50 of both the cell lines. Thus, these CLPNs are potentially useful for controlled drug delivery in the case of advanced chemotherapeutic applications.

Alapour, Saba; Ramjugernath, Deresh; Koorbanally, Neil A.

doi: 10.1039/c5ra18897kpmid: N/A

Synthesis of different chiral fluorinated Boc-[1,4]benzoxazins from their open chain precursors were investigated. The NMR spectra and crystallographic data showed the presence of the Smiles Rearrangement (SR) followed by copper catalysed coupling. The influence of the Boc protecting group, solvent, base, catalyst and the conformational changes of adducts was explored in detail by careful reaction optimization. No product was obtained in the absence of Boc, indicating its crucial role. Finally, a new mechanism for the SR copper catalysed ring closure was proposed.

Wu, Jinzhu; Dai, Jun; Shao, Yanbin; Sun, Yanchun

doi: 10.1039/c5ra13119gpmid: N/A

Novel fluorescent silicon quantum dots (Si-QDs) were synthesized by a one-step hydrothermal procedure using (3-aminopropyl)trimethoxysilane (APTES) as a silicon source and sodium ascorbate (SA) as a reducing agent. This synthetic strategy is straightforward, efficacious and low-cost. The as-synthesized Si-QDs featured narrow size distribution, intense purple-blue fluorescence with a photoluminescence quantum yield (PL QY) of 21%, complete water solubility, and favorable biocompatibility. Moreover, the resultant Si-QDs present robust stability in different circumstances, such as for long-term storage in air, in a wide pH range of 2–12 and under continuous UV irradiation, and they also do not respond to some metal ions. Their superior stability and safety render Si-QDs applicable as fluorescent probes in biomedical applications. The use of Si-QDs as an optical probe is illustrated by fluorescent imaging of IE8 cells.

Song, Ting Ting; Yang, Ming; Callsen, Martin; Wu, Qing Yun; Zhou, Jun; Wang, Shao Feng; Wang, Shi Jie; Feng, Yuan Ping

doi: 10.1039/c5ra16621gpmid: N/A

The exfoliation of graphene triggered dramatic interest to explore other two-dimensional materials for functionalizing future nanoelectronic devices. In this study, via first-principles calculations, we predict a stable planar Y2O3 (111) monolayer with a direct band gap of 3.96 eV. This high-κ dielectric monolayer can be further stabilized by a graphene substrate. The interaction between the planar Y2O3 (111) monolayer and graphene is found to be weak and dominated by van der Waals interactions, while the electronic properties are determined by orbital hybridization and electrostatic interaction. Our results indicate that a high-κ dielectric monolayer can be formed on a substrate with weak interfacial interaction via a physical deposition process, and this sheds light on engineering extremely thin high-κ dielectrics on graphene-based electronics with desired properties.

Yu, Jun; Si, Zhichun; Zhu, Man; Wu, Xiaodong; Chen, Lei; Weng, Duan; Zou, Jinshuo

doi: 10.1039/c5ra10653bpmid: N/A

A ZP/CZ (zirconium phosphate/Ce0.5Zr0.5O2) catalyst exhibits over 80% NOx conversion from 250 to 450 °C under a high GHSV of 300 000 h−1 in the presence of H2O, CO2 and C3H8. Mixing with soot leads to a decrease in NOx conversion of the catalyst at temperatures higher than 350 °C. After hydrothermal aging (760 °C for 48 h) and sulfur aging (400 °C for 48 h), ZP/CZ still possesses over 80% NOx conversions in 289–450 °C and 297–466 °C respectively, which are significantly better than those of home made Cu-SAPO-34 and vanadium catalysts at higher temperatures. These results indicate that ZP/CZ is a promising catalyst for NOx abatement for diesel engine exhausts.

Nedjari, S.; Hébraud, A.; Eap, S.; Siegwald, S.; Mélart, C.; Benkirane-Jessel, N.; Schlatter, G.

doi: 10.1039/c5ra15931hpmid: N/A

Electrostatic Template-Assisted Deposition (ETAD) of microparticles is described as a new process to control the deposition of microparticles by electrospraying onto a substrate. It relies on the construction of an electrostatic template by electrospinning a thin layer of fibers onto a micropatterned collector. Because the fibers cannot release their charges when they are suspended over cavities of the micropatterned collector, an electrostatic template is formed with repulsive and attractive domains. This electrostatic template is then used to guide precisely the particle deposition during the electrospraying step. Microstructured bi-layer composites with a great variety of micropatterns can thus be elaborated with any kind of materials allowing the use of the ETAD process for a wide range of applications. As a proof of concept, the ETAD process was applied for the production of composite scaffolds with poly(ε-caprolactone) nanofibers covered by a micropatterned layer of hydroxyapatite. This scaffold was then embedded in a biochip containing 21 wells and used for MG-63 cell proliferation and mineralization studies, showing their possible application in the screening of the scaffold structure for tissue engineering.

Ashraf, Uzma; Chat, Oyais Ahmad; Maswal, Masrat; Jabeen, Suraya; Dar, Aijaz Ahmad

doi: 10.1039/c5ra13002fpmid: N/A

The effect of sodium cholate (NaC) on the micellization and gelation characteristics of Pluronic P123 in aqueous media has been explored using tensiometry, rheology, dynamic light scattering (DLS), and densitometry. The aggregation characteristics were altered drastically with the addition of NaC as signified by an increase in the critical micelle concentration (CMC), critical micellization temperature (CMT) and critical gelation temperature (CGT). The results were explained on the basis of electrostatic and steric destabilization of P123 micelles by NaC. The apparent hydrodynamic diameter (DH) of P123 + NaC binary systems decreased upon addition of NaC up to 1.5 wt%. Further, in addition to an increase in DH, the presence of two types of scattering species was also evidenced with increase in NaC concentration from 2.5–10 wt%. The effect of NaC on the encapsulating capacity of P123 was also studied using naproxen and pyrene as two model hydrophobes. The work could give a sound understanding about the interaction and self-assembling behavior of Pluronics with the important physiological component i.e., bile salts which is important to consider in any pharmaceutical formulation involving Pluronics as drug delivery agents.