Rasel Das

Synergic effect of tungstophosphoric acid and sonication for rapid synthesis of crystalline nanocellulose

The utilization of sonication in combination with tungstophosphoric acid (PWA) catalyst reduces dramatically the time of operations from 30h to 10min by using an optimum sonication power of 225W. The basic cellulosic structure is maintained, allowing preparing high-quality nanocellulose. The size of the nanocellulose obtained was in the range from 15 to 35nm in diameter and several hundred nanometers in length, with a high crystallinity of about 88%. The nanocellulose shows a surface charge of -38.2mV which allows to obtaina stable colloidal suspension. The surface tension of the stable, swollen aqueous nanocellulose was close to that of water. These characteristics, together with the fast procedure allowed from the synergic combination of PWA and sonication, evidence the high potential of the proposed method for the industrial production of nanocellulose having the properties required in many applications.

Highly Efficient and Stable Novel NanoBiohybrid Catalyst to Avert 3,4-Dihydroxybenzoic Acid Pollutant in Water.

The present study reported for the first time covalent immobilization of protocatechuate 3,4-dioxygenase (3,4-POD) onto functionalized multi-walled carbon nanotubes (F-MWCNT) for degrading the toxic 3,4-dihydroxybenzoic acid (3,4-DHBA) pollutant in water. The F-MWCNTs had a maximum 3,4-POD loading of 1060 μg/mg. Immobilized 3,4 POD had 44% of relative structural changes to its free configurations. Nevertheless, >90% of relative activity and about 50% of catalytic efficiency were retained to the free enzyme. Immobilized 3,4-POD demonstrated higher alkaline stability and thermostability than the free 3,4-POD. The free and immobilized 3,4-POD lost 82% and 66% of relative activities, respectively after 180 min of incubations at 90 °C. Excellent shelf-life was observed for the immobilized 3,4-POD with residual activity of 56% compared with 41% and 39% of the free 3,4-POD at 4 °C and 25 °C over 30 days storage. Immobilized 3,4-POD showed >60% of catalytic activity retention even after ten-cycle uses, defraying the expenses of free 3,4-POD productions for long term uses. Finally, the immobilized 3,4-POD removed 71% of 3,4-DHBA from water in <4 h, paving its future application for water purification with reduced costs and time.

A Tractable Method for Measuring Nanomaterial Risk Using Bayesian Networks

While control banding has been identified as a suitable framework for the evaluation and the determination of potential human health risks associated with exposure to nanomaterials (NMs), the approach currently lacks any implementation that enjoys widespread support. Large inconsistencies in characterisation data, toxicological measurements and exposure scenarios make it difficult to map and compare the risk associated with NMs based on physicochemical data, concentration and exposure route. Here we demonstrate the use of Bayesian networks as a reliable tool for NM risk estimation. This tool is tractable, accessible and scalable. Most importantly, it captures a broad span of data types, from complete, high quality data sets through to data sets with missing data and/or values with a relatively high spread of probability distribution. The tool is able to learn iteratively in order to further refine forecasts as the quality of data available improves. We demonstrate how this risk measurement approach works on NMs with varying degrees of risk potential, namely, carbon nanotubes, silver and titanium dioxide. The results afford even non-experts an accurate picture of the occupational risk probabilities associated with these NMs and, in doing so, demonstrated how NM risk can be evaluated into a tractable, quantitative risk comparator.

Can We Optimize Arc Discharge and Laser Ablation for Well-Controlled Carbon Nanotube Synthesis?

Although many methods have been documented for carbon nanotube (CNT) synthesis, still, we notice many arguments, criticisms, and appeals for its optimization and process control. Industrial grade CNT production is urgent such that invention of novel methods and engineering principles for large-scale synthesis are needed. Here, we comprehensively review arc discharge (AD) and laser ablation (LA) methods with highlighted features for CNT production. We also display the growth mechanisms of CNT with reasonable grassroots knowledge to make the synthesis more efficient. We postulate the latest developments in engineering carbon feedstock, catalysts, and temperature cum other minor reaction parameters to optimize the CNT yield with desired diameter and chirality. The rate limiting steps of AD and LA are highlighted because of their direct role in tuning the growth process. Future roadmap towards the exploration of CNT synthesis methods is also outlined.

Cellulase biocatalysis: key influencing factors and mode of action

Commercial interests have been escalating worldwide on cellulase enzymes, since it has enormous potentiality to process most abundant and eco-friendly celluloses and convert them into the renewable and sustainable energy, chemicals, fuels and materials. However, overcoming the cellulose recalcitrance and understanding accurate cellulase catalytic activities have been remaining as major technological challenges. Here we reviewed cellulose hierarchy as a primary focus for cellulase actions and highlighted open questions related to endo- and exo-type cellulases. Special importance has been paid to critically evaluate research efforts on enzyme–substrate interactions, processivity, synergism and mechanistic paradigm for cellulose depolymerizations. These understandings pave the way for enzyme based cellulose bioprocessing and further gains of fundamental science and improved methods for cellulase engineering. We hope the article is potentially important for the biologists, polymer specialists, industrialists and most of the scientists active in cellulose science and technology.

Carbon Nanotubes Characterization by X-ray Powder Diffraction A Review

Carbon nanotubes have been increasingly used in the fields of nanorobotics, electrochemical catalysis, microarray chips, and green adsorbents for pollutants, sensors and optoelectronics. Complicated physico-chemical aspects and novel schemes to synthesize controlled featured carbon nanotubes have added new ambiguities to their characterizations and applications and these must be resolved on an urgent basis. Most of the characterization tools such as scanning electron microscopy, transmission electron microscopy, scanning tunneling microscopy and atomic force microscopy probes only for characterizing the local features of carbon nanotubes. However, X-ray powder diffraction can reveal the local and global features of microstructure’s lattice and crystalline phases, domain sizes, and impurities. Thus it is worthwhile to highlight this technique for better understanding and utilization of its benefit to unravel the carbon nanotube ambiguities. To the best of our knowledge, no comprehensive reviews or systematic description of X-ray powder diffraction on carbon nanotubes characterization have been published yet. In this review, we filled-up this gap and provided a systematic presentation of X-ray powder diffraction application in carbon nanotubes characterization. This could be used as a reference guide for the utilization of X-ray powder diffraction to probe the various features of carbon nanotubes and carbon nanotubes based materials.

Common wet chemical agents for purifying multiwalled carbon nanotubes

Purification and functionalization of multiwalled carbon nanotubes (MWCNTs) are challenging but vital for their effective applications in various fields including water purification technologies, optoelectronics, biosensors, fuel cells, and electrode arrays. The currently available purification techniques, often complicated and time consuming, yielded shortened and curled MWCNTs that are not suitable for applications in certain fields such as membrane technologies, hybrid catalysis, optoelectronics, and sensor developments. Here we described the H2O2 synergy on the actions of HCl and KOH in purifying and functionalizing pristine MWCNTs. The method (HCl/H2O2) showed 100% purification yield as compared to HCl and KOH/H2O2 with purification yields 93.46 and 3.92%, respectively. We probed the findings using transmission electron microscope, energy dispersive X-ray spectroscope, attenuated total reflectance infrared spectroscope, Raman spectroscope, thermal gravimetric analysis, and X-ray powder diffraction. The study is a new avenue for simple, rapid, low cost, and scalable purification of pristine MWCNTs for application in versatile fields.

Multifunctional Carbon Nanotubes (CNTs): A New Dimension in Environmental Remediation

Water pollution is a serious, persistent and emerging problem not only in Malaysia but all over the world. It has negative impacts on the sustainability of water resources, aquatic flora and fauna and community health. It significantly reduces total water availability because of the lack of suitable and cost-effective pollutant treatment facilities. Current facilities for water purification are time consuming, expensive and have low affinity and efficiency to newly emerging micro pollutants in water. Carbon nanotube (CNT) based nanocomposites and hybrids have attracted huge attention for their potential in the treatment of newly emerging micropollutants in water bodies. Addition of various molecules and binders such as magnetic nanoparticles, pollutant binding and degrading receptors and enzymes has added new dimensions in the fibrous shape, high aspect ratio, large surfaces, and accessible mesopores of CNTs. In this review, we have outlined the recent progress and future prospects of multifunctional CNT-hybrids for the treatment of both conventional priority and newly emerging micropollutants in water environment. The review also has highlighted the future strategies for overcoming the shortcomings of existing techniques and materials for water purification applications.

Molecular characterization of Cryptosporidium xiaoi in goat kids in Bangladesh by nested PCR amplification of 18S rRNA gene

Objective:To investigate the prevalence of Cryptosporidium spp.in goat kids in selected areas of Bangladesh and to elucidate the potential zoonotic hazards.Methods:In the present study,we have used Ziehl-Neelsen staining and nested PCR approach to identify and characterize the Cryptosporidium sp.from diarrhoeic feces of goat kids.A total of 100 diarrhoeic feces samples were collected from Chittagong region in Southern Bangladesh.For nested PCR analysis,specific primers for amplification of 581 base pair fragments of 18 S rRNA gene were used.Results:A total of 15%and 3%samples were found positive in microscopic study and in nested PCR analysis respectively.Phylogenetic analysis of sequence data showed similarity with that of Cryptosporidium xiaoi recorded from sheep and goat.Conclusions:To our knowledge,this is the first report of Cryptosporidium xiaoi responsible for diarrhoea in goat kids in Bangladesh.Further study can highlight their zoonotic significance along with genetic diversity in other host species inside the country.

Optimization of the Synthesis of Superhydrophobic Carbon Nanomaterials by Chemical Vapor Deposition

Demand is increasing for superhydrophobic materials in many applications, such as membrane distillation, separation and special coating technologies. In this study, we report a chemical vapor deposition (CVD) process to fabricate superhydrophobic carbon nanomaterials (CNM) on nickel (Ni)-doped powder activated carbon (PAC). The reaction temperature, reaction time and H2/C2H2 gas ratio were optimized to achieve the optimum contact angle (CA) and carbon yield (CY). For the highest CY (380%) and CA (177°), the optimal reaction temperatures were 702 °C and 687 °C, respectively. However, both the reaction time (40 min) and gas ratio (1.0) were found to have similar effects on CY and CA. Based on the Field emission scanning electron microscopy and transmission electron microscopy images, the CNM could be categorized into two main groups: a) carbon spheres (CS) free carbon nanofibers (CNFs) and b) CS mixed with CNFs, which were formed at 650 and 750 °C, respectively. Raman spectroscopy and thermogravimetric analysis also support this finding. The hydrophobicity of the CNM, expressed by the CA, follows the trend of CS-mixed CNFs (CA: 177°) > CS-free CNFs (CA: 167°) > PAC/Ni (CA: 65°). This paves the way for future applications of synthesized CNM to fabricate water-repellent industrial-grade technologies.