Structure, surface area and morphology of aluminas from thermal decomposition of Al(OH)(CH3COO)2 crystals

Sonochemical synthesis of aluminium and aluminium hybrids for remediation of toxic metals

Spherical shaped nano-size aluminium oxide and its hybrids with indole and indole derivatives have been synthesized using sol-gel and post grafting methods coupled with sonication (Branson Digital SonifierS-250D; 20 kHz; 40%) for the remediation of toxic metals (lead and mercury). Different spectroscopic techniques (FTIR, SEM, BET, XRD, and XPS) have been applied to assess the properties of synthesized aluminium oxide and its hybrids. FTIR spectra showed the absorption bands of aluminium oxide (Al-O-Al) and aluminium hybrids (Al-O-C) at 800-400 cm-1 and 1650-1100 cm-1 region, respectively. SEM showed spherical shaped clusters of aluminium oxide which changed into the net-shape structure after the hybrid synthesis. It is worth noting that sonication energy increases the total surface area of aluminium oxide when it gets hybridized with indole and its derivatives from 82 m2/g to 167 m2/g; it also improved the product yield from 68% to 78%. Simultaneously, FTIR, SEM and BET analysis of non-sonicated aluminium oxide and its hybrids were also recorded for comparison. While XRD and XPS analysis were only conducted for sonicated aluminium oxide and its hybrids to manifest the structural and compositional properties. XRD patterns indexed as the cubic crystal system with an average 41 nm crystallite size of sonicated aluminium oxide which remains unaffected after hybrid synthesis. A survey scan under XPS confirmed the presence of all expected elements (aluminium, oxygen, carbon, nitrogen) and deconvolution of each recorded peak showed binding of element with its neighboring elements. The performance of aluminium oxide and its hybrids synthesize with and without sonication are also evaluated using a time-dependent batch adsorption protocol optimize for one hour. The maximum adsorption of lead (37%) and mercury (40%) are found onto sonicated aluminium oxide. The sonicated aluminium hybrids showed 43-63% of lead and 55-67% of mercury at pH 7. The fitness of experimental data using adsorption kinetics and isotherms revealed that adsorption follows Pseudo-second-order kinetic, Langmuir, and Freundlich isotherms.

Towards Macroporous α-Al2O3-Routes, Possibilities and Limitations

This article combines a systematic literature review on the fabrication of macroporous α-Al₂O₃ with increased specific surface area with recent results from our group. Publications claiming the fabrication of α-Al₂O₃ with high specific surface areas (HSSA) are comprehensively assessed and critically reviewed. An account of all major routes towards HSSA α-Al₂O₃ is given, including hydrothermal methods, pore protection approaches, dopants, anodically oxidized alumina membranes, and sol-gel syntheses. Furthermore, limitations of these routes are disclosed, as thermodynamic calculations suggest that γ-Al₂O₃ may be the more stable alumina modification for A_BET > 175 m²/g. In fact, the highest specific surface area unobjectionably reported to date for α-Al₂O₃ amounts to 16-24 m²/g and was attained via a sol-gel process. In a second part, we report on some of our own results, including a novel sol-gel synthesis, designated as mutual cross-hydrolysis. Besides, the Mn-assisted α-transition appears to be a promising approach for some alumina materials, whereas pore protection by carbon filling kinetically inhibits the formation of α-Al₂O₃ seeds. These experimental results are substantiated by attempts to theoretically calculate and predict the specific surface areas of both porous materials and nanopowders.

Synthesis, spectroscopic and luminescence properties of Ga-doped γ-Al2O3

Gallium-doped aluminum oxide (Al_1-xGa_x)₂O₃ with γ-Al₂O₃ (spinel) structure has been synthesized by the precursor method using the formate Al_1-xGa_x(OH)(HCOO)₂ as a precursor. The examination of Al_1-xGa_x(OH)(HCOO)₂ (x = 0.0, 0.1, 0.2, 0.3, 0.4) was carried out by X-ray powder diffraction, Infrared, Raman spectroscopy and differential-thermal methods. The solid solutions γ-(Al_1-xGa_x)₂O₃ with х≤0.2 have been synthesized by thermolysis of precursors in helium atmosphere at 700 °C; they exhibit white-blue emission under UV excitation, whose intensity lowers with increasing dopant concentration. As an independent method, the DFT calculations confirmed thermodynamically the stability field of γ-(Al_1-xGa_x)₂O₃ solid solutions and the NMR data on relative abundance of Al and Ga within the tetrahedral and octahedral sites in the metal sublattice. Furthermore, the structural and thermodynamic properties of carbon-containing impurities within these compounds were suggested theoretically as possible models of luminescence emission centers. The experimentally observed Ga-dependent quenching of luminescence was explained using the competition between C2p and Ga4p states within the band gap of γ-Al₂O₃.

Enzyme Immobilized on Nanoporous Carbon Derived from Metal-Organic Framework: A New Support for Biodiesel Synthesis

In this study, nanoporous carbon (NPC) derived from metal-organic framework was used as support for the immobilization of Burkholderia cepacia lipase. The decorated aluminum oxide within the mesoporous NPC improved the enzyme loading efficiency as well as the catalytic ability for the transesterification of soybean oil, thus making it a promising green and sustainable catalytic system for industrial application.

Commercially manufactured engineered nanomaterials for environmental and health studies: important insights provided by independent characterization

Environmental and health studies on nanomaterials are appearing in the literature at a rapid pace. These studies will address important issues related to the environmental health and safety (EHS) of nanomaterials. As noted in many recent workshop and agency reports, studies devoted toward the environmental fate and transport, nanomaterial-biological interactions, toxicity, and overall risk assessment of nanomaterials should have nanomaterial characterization as a central component of the study design. This aspect of the study design is necessary so that risks associated with nanomaterials can be fully understood and related to specific material properties. For studies that use commercially manufactured nanomaterials, the company often provides characterization data (e.g., chemical composition, phase, and size) of the purchased materials. One question is, how good are these data? Another is, what methods of analysis are used to characterize the properties of commercial nanomaterials? In the present study, some examples are presented that show marked differences between independent characterization of commercially manufactured nanomaterials and that provided by the company. Furthermore, information provided by the manufacturer may be incomplete and nonrepresentative of the entire sample and, in some cases, the information can, in fact, be wrong. Thus, the current study demonstrates an important need for independent characterization data in EHS studies of purchased materials.