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Without nanosafety guidelines, the long-term sustainability of carbon nanotubes (CNTs) for water purifications is questionable. Current risk measurements of CNTs are overshadowed by uncertainties. New risks associated with CNTs are evolving through different waste water purification routes, and there are knowledge gaps in the risk assessment of CNTs based on their physical properties. Although scientific efforts to design risk estimates are evolving, there remains a paucity of knowledge on the unknown health risks of CNTs. The absence of universal CNT safety guidelines is a specific hindrance. In this paper, we close these gaps and suggested several new risk analysis roots and framework extrapolations from CNT-based water purification technologies. We propose a CNT safety clock that will help assess risk appraisal and management. We suggest that this could form the basis of an acceptable CNT safety guideline. We pay particular emphasis on measuring risks based on CNT physico-chemical properties such as diameter, length, aspect ratio, type, charge, hydrophobicity, functionalities and so on which determine CNT behaviour in waste water treatment plants and subsequent release into the environment.

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.

Low-cost production of nanocellulose from diverse lignocellulosic feedstocks has become an important topic for developing sustainable nanomaterials. The available feedstocks include both woody and non-woody plants, where the latter are relatively underutilized. Interestingly, the porous structure and low lignin content in most non-woody plants, such as agricultural residues and natural fibers, also makes them ideal sources for lower energy nanocellulose production using simpler methods than those required to process woody plants. To enhance the goal of circularity, this review first provides an overview of the nanocellulose conversion from cellulose and then comprehensively discusses the use of non-woody feedstocks for nanocellulose production. Specifically, the availability of suitable non-woody feedstocks and the use of low-cost processes for pulping and cellulose oxidation treatments, including alkaline, solvent pulping, and nitrogen-oxidation treatments, are discussed. The information in this review can lead to new opportunities to achieve greater sustainability in biobased economies. Additionally, demonstrations of nanocellulose-based water purification technologies using agricultural residues derived remediation materials are highlighted at the end of this review.

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 H 2 /C 2 H 2 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.

This text introduces carbon nanotubes as a matrix for efficient nanohybrid catalysis. The preparation and use of such materials in ultra-grade water purification is described. Simple chemical methods for purification and functionalisation of carbon nanotubes prior to their use is also detailed. The author also discusses the potential use of nanotube-based nanobiohybrid catalysts in the removal of organic pollutants.

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.

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.

Low-cost production of nanocellulose from diverse lignocellulosic feedstocks has become an important topic for developing sustainable nanomaterials. The available feedstocks include both woody and non-woody plants, where the latter are relatively underutilized. Interestingly, the porous structure and low lignin content in most non-woody plants, such as agricultural residues and natural fibers, also makes them ideal sources for lower energy nanocellulose production using simpler methods than those required to process woody plants. To enhance the goal of circularity, this review first provides an overview of the nanocellulose conversion from cellulose and then comprehensively discusses the use of non-woody feedstocks for nanocellulose production. Specifically, the availability of suitable non-woody feedstocks and the use of low-cost processes for pulping and cellulose oxidation treatments, including alkaline, solvent pulping, and nitrogen-oxidation treatments, are discussed. The information in this review can lead to new opportunities to achieve greater sustainability in biobased economies. Additionally, demonstrations of nanocellulose-based water purification technologies using agricultural residues derived remediation materials are highlighted at the end of this review.

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.

A novel technique for the covalent attachment of a light-responsive spiropyran onto polyamide thin film composite nanofiltration (NF) membranes in a one-step reaction using low-energy electron beam technology is described. The effect of illumination of the immobilized spiropyran was studied, as well as the resulting membrane properties with respect to MgSO4 retention, water permeability rate, and chlorine resistance. Electron beam irradiation showed a direct effect on the transformation of the rough PA NF membrane surface into a ridge-and-valley structure. Upon UV light irradiation, the spiropyran transformed into zwitterionic merocyanine, which had shown MgSO4 removal of >95% with water permeation rates of 6.5 L/(m2·h·bar). Alternatively, visible light was used to convert merocyanine to spiropyran, which achieved >95% of MgSO4 retention with a water flux of around 5.25 L/(m2·h·bar). The modified NF membranes showed higher chlorine resistance as well as a higher normalized water flux as compared to the reference membrane, without a loss of ion retention. All the NF membranes were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. This study demonstrates a simple and inexpensive method for the immobilization of molecules onto polymeric membranes, which may be applied in water softening.