Adil Majeed Rather

Sustainable polymeric material for the facile and repetitive removal of oil-spills through the complementary use of both selective-absorption and active-filtration processes

Oil contamination in aqueous phases by regular industrial discharges and accidental oil spillages during the production and transportation of oil is emerging as a global challenge due to its catastrophic effect on the aquatic ecosystem. Here, a naturally abundant fibrous substrate (i.e., a cotton ball) is strategically exploited in the energy-efficient and environmentally-friendly cleaning of different forms of oil-contamination, including floating light-oil, and sedimentary heavy-oil and emulsions, after the appropriate optimization of both the topography and the essential chemistry of the fibrous substrate through a catalyst-free, simple and scalable 1,4-conjugate addition reaction between amine and acrylate groups under ambient conditions. The synthesized superhydrophobic cotton (SHC), that is capable of extreme repellence of water both in air and under oil, has provided a single avenue for both highly selective (1) absorption (with an efficiency above 2000 wt% for both heavy and light oils) and (2) gravity-driven active filtration of oil. The synthesized material is highly efficient in the separation of oil from aqueous phases that are chemically harsh, including extremes of pH (1 & 12), artificial seawater, etc. The embedded superhydrophobicity in the synthesized material remained unperturbed, even after prolonged (10 days) exposure to UV irradiation (both at 254 nm and 365 nm) and after incurring various physical deformations. Although this synthesized material was repeatedly (100 times) used in removing oil contamination, the antifouling property remained intact with an advancing water contact angle of 157° and the oil/water separation efficiency remained around 95%. Further, the current approach provided a simple basis to separate oil from a complex three-phase oil/water mixture that was composed of a heavy-oil phase (the bottom layer), an aqueous phase (the middle layer), and a light-oil phase (the top layer), where the strategic application of SHC allowed the successful clean-up of oils through the complementary use of absorption and filtration processes.

Exceptional control on physical properties of a polymeric material through alcoholic solvent-mediated environment-friendly Michael addition reaction

Alcoholic solvents that are used as media for environment-friendly Michael addition reaction are strategically exploited to control various physical properties of a polymeric material, including shrinkage, flexibility and special wettability: adhesive and ultra-non-adhesive superhydrophobicity. An appropriate selection of the alcoholic solvent provided the material with highly flexible, durable and moldable superhydrophobic monolith, which can be even physically deformed (75%) repetitively without any negative impact on its physical or chemical integrity.

Strategic Formulation of Graphene Oxide Sheets for Flexible Monoliths and Robust Polymeric Coatings Embedded with Durable Bioinspired Wettability

Artificial bioinspired superhydrophobicity, which is generally developed through appropriate optimization of chemistry and hierarchical topography, is being recognized for its immense prospective applications related to environment and healthcare. Nevertheless, the weak interfacial interactions that are associated with the fabrication of such special interfaces often provide delicate biomimicked wettability, and the embedded antifouling property collapses on exposure to harsh and complex aqueous phases and also after regular physical deformations, including bending, creasing, etc. Eventually, such materials with potential antifouling property became less relevant for practical applications. Here, a facile, catalyst-free, and robust 1,4-conjugate addition reaction has been strategically exploited for appropriate covalent integration of modified graphene oxide to developing polymeric materials with (1) tunable mechanical properties and (2) durable antifouling property, which are capable of performing both in air and under oil. Furthermore, this approach provided a facile basis for (3) engineering a superhydrophobic monolith into arbitrary free-standing shapes and (4) decorating various flexible (metal, synthetic plastic, etc.) and rigid (glass, wood, etc.) substrates with thick and durable three-dimensional superhydrophobic coatings. The synthesized superhydrophobic monoliths and polymeric coatings with controlled mechanical properties are appropriate to withstand different physical insults, including twisting, creasing, and even physical erosion of the material, without compromising the embedded antiwetting property. The materials are also equally resistant to various harsh chemical environments, and the embedded antifouling property remained unperturbed even after continuous exposure to extremes of pH (pH 1 and pH 11), artificial sea water for a minimum of 30 days. These flexible and formable free-standing monoliths and stable polymeric coatings that are extremely water-repellent both in air and under oil, are of utmost importance owing to their suitability in practical circumstances and robust nature.

Synthesis of fish scale and lotus leaf mimicking, stretchable and durable multilayers

In general, nature inspired water (lotus leaf mimicking superhydrophobicity in air) and oil (fish scale-inspired superoleophobicity under water) repellent interfaces that are associated with specific physical and chemical parameters, are developed by adopting separate synthesis processes. However, a slight perturbation of the essential topography and chemistry is likely to cause permanent damage to these two distinct nature inspired artificial wettabilites. In this paper, two distinctly characteristic nanomaterials—flexible graphene oxide nanosheets (with grafted primary amine moieties) and amine reactive polymeric nanocomplexes (with residual acrylate groups), are covalently and strategically integrated through a 1,4-conjugate addition reaction for adopting both the fish scale- and lotus leaf inspired ‘stretchable’ and durable wettability that is capable of sustaining: (a) large tensile deformation (100%) multiple times (500 times), and, (b) severe physical/chemical exposures—including physical erosion of the polymeric coating, prolonged exposure to extremes of pH, salinity, ultraviolet radiation, physical manipulations, and so on. The covalent integration of these two different nanomaterials provided a single and simple method for adopting appropriate topography and essential chemical functionality that conferred durable superhydrophobicity and underwater superoleophobicity. The synthesized bio-mimicking interfaces remained water/oil repellent even after stretching the physically damaged multilayer interfaces. Such a durable material is deposited on various substrates, and thus, would be of potential interest for diverse prospective applications in practically relevant harsh applications. Furthermore, there are very few reports of such a single chemical approach that provided durable and stretchable nature inspired superhydrophobicity (in air) and superoleophobicity (under water), in the literature.

Alkali metal-ion assisted Michael addition reaction in controlled tailoring of topography in a superhydrophobic polymeric monolith

In general, lotus leaf and rose petal-inspired wettabilities are artificially developed through the integration of hierarchical topography and essential chemical functionality. However, a fundamental and important aspect of this nature inspired wettability is not yet addressed; between the hierarchical topography and essential chemical modulation, which is the more sensitive parameter for this nature inspired special wettability? The design of a common approach for tailoring both the hierarchical topography and chemical functionalities is highly essential for investigating such a relevant fundamental aspect; however the synthesis of such a material is extremely difficult in reality. In the current computational study, the Michael addition reaction between unsaturated ester and primary amine groups was found to be facilitated in the presence of alkali metal ions. Interestingly, the mixture of branched polyethyleneimine (BPEI) and dipentaerythritol pentaacrylate (5Acl) in ethanol transformed into a chemically reactive polymeric monolith with tailored hierarchical features—based on the selection of appropriate alkali metal ions in the reaction mixture. The current study investigates the impact of the change in hierarchy in the topography on the nature inspired super-wettability—keeping the chemical functionality of the hierarchical topography intact. On the other hand, the inherent chemical reactivity of the hierarchical interfaces allowed us to examine the change in the chemical modulation—independently and precisely. The post-covalent modification of the hierarchical topography with longer and shorter hydrocarbon tails has a significant impact in controlling the metastable trapped air in the artificially biomimicked interfaces, and eventually controls the Wenzel, Cassie–Baxter and Cassie–Wenzel transition states. This current approach also allows us to modulate other relevant physical properties in the material—including the shrinkage of the material after the removal of the reaction solvent and compressive modulus. The materials with optimized physical properties were successfully exploited in the separation and collection of different forms of oil spills through both selective absorption process and gravity driven filtration process, even under practically relevant severe settings. Such a facile and general approach for tailoring both the chemical functionality and topography could be of potential interest for developing various functional and smart materials—including tissue engineering, patterned interfaces, etc.

Aloe Vera Mucilage Derived Highly Tolerant Underwater Superoleophobic Coating

Aloe vera mucilage (AVM), which mainly consists of an immobilized aqueous phase, is strategically exploited for achieving an extremely oil repellent and durable coating. The nature-inspired coating that is derived from AVM and appropriately modified through Michael addition reaction is capable of sustaining various challenging chemical (pH 1, pH 12, surfactant water, sea water, and river water) and physical (150% tensile deformation, scratching and other abrasions) exposures—without compromising the embedded underwater superoleophobicity. Further, this material was successfully exploited for gravity-driven and eco-friendly separation of oil/water mixtures—in various severe practically relevant physical and chemical circumstances.