M.P. Srinivasan

Novel activation process for preparing highly microporous and mesoporous activated carbons

Abstract An improved ZnCl 2 -chemical activation method is proposed to produce highly porous activated carbons. The novel process can produce either microporous carbons or mesoporous carbons from lignocellulosic materials, such as coconut shells and palm seeds. The porosity of the resultant activated carbons was characterized by nitrogen adsorption isotherms at 77 K. The BET-surface area of the carbons can be over 2400 m 2 /g; the mesopore content (ratio of mesopore volume to total pore volume) is 71%. Furthermore, the activated carbon from palm seeds possesses mesopore content as high as 94%. Thermogravimetric analysis (TGA) was used to monitor the course of pyrolysis of coconut shell and ZnCl 2 -impregnated coconut shell. The adsorptive properties for phenol and dyes were tested.

Mesoporous high-surface-area activated carbon

Coconut shells and palm seeds have been used as raw materials to obtain activated carbons with high surface area by simultaneous treatment with zinc chloride and carbon dioxide as the physical and chemical agents, respectively. Both the surface area and the mesopore content could be tuned by controlling the experimental parameters, viz., ZnCl2-to-raw material ratio, duration of exposure to the carbon dioxide atmosphere and temperature of activation. In particular, ZnCl2-to-shell ratios above 1 yielded high surface areas, and ratios above 2 resulted in high mesopore content. The adsorption capacity and nature of the porosity were investigated by adsorption experiments using adsorbates with different molecular sizes (viz., phenol, methylene blue and erythrosine red). The capacities of the mesoporous activated carbons were much higher than those of microporous carbons for larger adsorbates, confirming the presence of large amounts of mesopores in the former. The measured adsorption capacities for the prepared samples conformed to the expectations based on micropore and mesopore area and volume estimations.

Activated carbons derived from coconut shells as high energy density cathode material for Li-ion capacitors

In this manuscript, a dramatic increase in the energy density of ~ 69 Wh kg−1 and an extraordinary cycleability ~ 2000 cycles of the Li-ion hybrid electrochemical capacitors (Li-HEC) is achieved by employing tailored activated carbon (AC) of ~ 60% mesoporosity derived from coconut shells (CS). The AC is obtained by both physical and chemical hydrothermal carbonization activation process, and compared to the commercial AC powders (CAC) in terms of the supercapacitance performance in single electrode configuration vs. Li. The Li-HEC is fabricated with commercially available Li4Ti5O12 anode and the coconut shell derived AC as cathode in non-aqueous medium. The present research provides a new routine for the development of high energy density Li-HEC that employs a mesoporous carbonaceous electrode derived from bio-mass precursors.

Unveiling TiNb2O7 as an Insertion Anode for Lithium Ion Capacitors with High Energy and Power Density

This is the first report of the utilization of TiNb2 O7 as an insertion-type anode in a lithium-ion hybrid electrochemical capacitor (Li-HEC) along with an activated carbon (AC) counter electrode derived from a coconut shell. A simple and scalable electrospinning technique is adopted to prepare one-dimensional TiNb2 O7 nanofibers that can be characterized by XRD with Rietveld refinement, SEM, and TEM. The lithium insertion properties of such electrospun TiNb2 O7 are evaluated in the half-cell configuration (Li/TiNb2 O7 ) and it is found that the reversible intercalation of lithium (≈3.45 mol) is feasible with good capacity retention characteristics. The Li-HEC is constructed with an optimized mass loading based on the electrochemical performance of both the TiNb2 O7 anode and AC counter electrode in nonaqueous media. The Li-HEC delivers very high energy and power densities of approximately 43 Wh kg(-1) and 3 kW kg(-1) , respectively. Furthermore, the AC/TiNb2 O7 Li-HEC delivers a good cyclability of 3000 cycles with about 84% of the initial value.

Thermogravimetric investigation of hydrochar-lignite co-combustion

Co-combustion of hydrochar with lignite was investigated by means of thermogravimetric analysis. Hydrochars were produced from coconut fibers and eucalyptus leaves under hydrothermal conditions at 250°C. The hydrochar was added in varying amounts to lignite for combustion. The results indicated that hydrothermal treatment decreased the volatile matter content and increased the fixed carbon content of the biomaterials. The elevated energy density and decreased ash content of the hydrochar improved its combustion behavior when co-fired with lignite for energy production. The hydrochars derived from coconut fiber and eucalyptus leaves had similar chemical compositions and showed similar influences on lignite combustion. Hydrochar addition increased the burnout and shortened the combustion range of the hydrochar-lignite blends. High combustion efficiency was observed due to the synergistic interactions between hydrochar and lignite during the co-combustion process. A kinetic study showed that the combustion process of hydrochar-lignite blends followed first-order reaction rates.

A simple method for developing mesoporosity in activated carbon

Abstract A simple process was proposed based on a combination of chemical and physical activation for the production of activated carbon. The process was expected to improve the mesoporosity in activated carbons. The KOH- or ZnCl 2 -chemical activation coupled with CO 2 -physical activation of lignocellulosic materials, such as coconut shells and palm stones, were used as a simultaneously chem-physical activation for increasing the mesoporosity. The porosity of the resultant activated carbons was characterized by nitrogen adsorption isotherms at 77 K. Both chemicals and CO 2 had effects on the formation of mesopores. Intensified activation conditions, such as high chemical ratio to the precursors, long soaking time, elevated temperature, increased the mesoporosity in activated carbons. The surface area and the nature of the porosity can be controlled by means of the experimental parameters. By changing the ratio of activating agent to carbon precursor, it is possible to control the pore size from supermicropore (1.5–2.0 nm) to mesopore (2–3.49 nm). The BET-surface area of the carbons can be over 2100 m 2 /g; the mesopore content (ratio of mesopore volume to total pore volume) is 71%. Furthermore, the activated carbon from palm stones possesses mesopore content as high as 94%.

Enhanced super-hydrophobic and switching behavior of ZnO nanostructured surfaces prepared by simple solution – Immersion successive ionic layer adsorption and reaction process

A simple and cost-effective successive ionic layer adsorption and reaction (SILAR) method was adopted to fabricate hydrophobic ZnO nanostructured surfaces on transparent indium-tin oxide (ITO), glass and polyethylene terephthalate (PET) substrates. ZnO films deposited on different substrates show hierarchical structures like spindle, flower and spherical shape with diameters ranging from 30 to 300 nm. The photo-induced switching behaviors of ZnO film surfaces between hydrophobic and hydrophilic states were examined by water contact angle and X-ray photoelectron spectroscopy (XPS) analysis. ZnO nanostructured films had contact angles of ~140° and 160°±2 on glass and PET substrates, respectively, exhibiting hydrophobic behavior without any surface modification or treatment. Upon exposure to ultraviolet (UV) illumination, the films showed hydrophilic behavior (contact angle: 15°±2), which upon low thermal stimuli revert back to its original hydrophobic nature. Such reversible and repeatable switching behaviors were observed upon cyclical exposure to ultraviolet radiation. These biomimetic ZnO surfaces exhibit good anti-reflective properties with lower reflectance of 9% for PET substrates. Thus, the present work is significant in terms of its potential application in switching devices, solar coatings and self-cleaning smart windows.

Self-assembled organic thin films on electroplated copper for prevention of corrosion

Self-assembled organic thin films of dodecanethiol (DT), mercaptobenzothiazole (MBT), benzotriazole (BTA), imidazole (IMD) and benzothiazole (BT) are formed by adsorption on the surface of copper thin film used in ultralarge-scale integrated circuits. The films are characterized by x-ray photoelectron spectroscopy. The inhibition of corrosion of these organic thin films is investigated in aerated 0.5 M H2SO4 solutions by electrochemical impedance spectroscopy and potentiodynamic polarization techniques. The presence of these films reduced corrosion by blocking the copper surface from the oxygen dissolved in the acid medium. The relative inhibition efficiencies of these inhibiting agents in preventing copper oxidation are found to be in the order of DT>MBT>BT>BTA>IMD. The effectiveness of the inhibitors increased with the temperature, concentration of the inhibitors, and duration of immersion in the solution. An adsorption model is proposed on the basis of variation of the impedance according to the inhibi...

Coaxial electrohydrodynamic atomization: microparticles for drug delivery applications.

As cancer takes its toll on human health and well-being, standard treatment techniques such as chemotherapy and radiotherapy often fall short of ideal solutions. In particular, adverse side effects due to excess dosage and collateral damage to healthy cells as well as poor patient compliance due to multiple administrations continue to pose challenges in cancer treatment. Thus, the development of appropriately engineered drug delivery systems (DDS) for effective, controlled and sustained delivery of drugs is of interest for patient treatment. Moreover, the physiopathological characteristics of tumors play an essential role in the success of cancer treatment. Here, we present an overview of the application of double-walled microparticles for local drug delivery with particular focus on the electrohydrodynamic atomization (EHDA) technique and its fabrication challenges. The review highlights the importance of a combination of experimental data and computational simulations for the design of an optimal delivery system.

Hydrothermal pre-treatment for mesoporous carbon synthesis: enhancement of chemical activation

This work presents a resource-friendly process to produce high surface area mesoporous activated carbons from biomass. ZnCl2 as an activating agent was incorporated into the biomass (coconut shells) during a hydrothermal pre-treatment step. The pre-treatment was followed by pyrolysis accompanied by physical activation. The resultant mesoporous activated carbons possessed a higher total surface area and a greater degree of mesoporosity compared to the biomass that was pyrolysed without hydrothermal treatment. The cause of higher mesoporosity is inferred to be the more conducive environment for accessibility of ZnCl2 due to reduced diffusion resistance to the biomass provided by the hydrothermal treatment. In addition, the hydrothermal environment facilitated the generation of oxygen-containing functional groups that contributed to the enhanced activity of ZnCl2. Up to 67% increase in the mesoporous surface area was achieved with the inclusion of the pre-treatment step. Analogously, 50% more ZnCl2 was required to deliver the same performance in the absence of the pre-treatment step. The mesoporous activated carbons were tested for adsorption of textile dyes and possessed high adsorption capacities of up to 526 mg and 630 mg per g of carbon for methylene blue and erythrosine red, respectively. The incorporation of the hydrothermal pre-treatment is an important step in developing processes for converting biomass that make efficient and effective use of activating agents.