Sustainable nanotechnology has made substantial contributions in providing contaminant-free water to humanity. In this Review, we present the compelling need for providing access to clean water through nanotechnology-enabled solutions and the large disparities in ensuring their implementation. We also discuss the current nanotechnology frontiers in diverse areas of the clean water space with an emphasis on applications in the field and provide suggestions for future research. Extending the vision of sustainable and affordable clean water to environment in general, we note that cities can live and breathe well by adopting such technologies. By understanding the global environmental challenges and exploring remedies from emerging nanotechnologies, sustainability in clean water can be realized. We suggest specific pointers and quantify the impact of such technologies.

This is due to the fact that at any given moment, the earth's atmosphere contains an astounding 37.5 million billion gallons of water as vapor, [2] and an efficient device to capture a fraction of this water vapor, in a cost-effective way would help solve the water crisis.Over the period of human existence, it has become apparent that biomimicking is the most efficient way to tackle such problems. When we look into nature, there are organisms, which in the course of evolution have acquired physical traits that enabled them to capture atmospheric water, even in the most arid corners of our planet. One such example is the Stenocara beetle of Namib Desert which capture water on its hardened forewings. [3] Electron microscopic images of these have revealed unique array of hydrophilic regions distributed on a superhydrophobic background, [4] creating a surface energy gradient, which facilitates efficient condensation and transportation of atmospheric water. Another such example is spider silk, which shows unique periodic spindle-knot structure when wetted and efficiently collects water from atmosphere through the combination of surface energy gradient and Laplace pressure difference. Other inspirations from nature are some cactaceae species which live in arid environments and are extremely drought-tolerant. [5] These species are shown to have structures with spines and trichomes which enable them to condense humidity efficiently from the atmosphere. Grasslands are also examples of natural atmospheric water harvesters. Hence, micro/nanostructuring of the water-collecting surface plays a critical role in determining the efficiency of water capture. With the advancement of nanotechnology, significant efforts have been directed toward fabricating surfaces with similar morphological features and chemical patterning to enable efficient water capture. [6,7] However, these natural and nature-mimicked surfaces collect atmospheric water in the form of dew/fog and require the temperature to drop below the dew point to cause condensation. For building a practical and round-the-clock operating atmospheric water generator, it is important to cool the condensing surfaces and the surrounding air efficiently, with minimum energy input. Heat transfer efficiency of the condensing surface material is as important as the water transfer efficiency for creating a viable radiative condenser. Although many biomimetic, patterned surfaces have been made for fog collection, inspired by active condensing Water scarcity is one of the most alarming problems of the planet. An ambient ion based method is developed to make hydrophilic-hydrophobic patterned silver nanowires (NWs) as humidity harvesters of unprecedented efficiency. Such water harvesters are developed by two-step surface modification of the as-synthesized NWs (known from a report earlier) using electrospray. These patterned NWs of ≈20 µm length and ≈200 nm width grown over a relatively large area (2 × 2 cm 2 ) exhibit atmospheric water capture (AWC) efficiency of 56.6 L m −2 d −1 , the...

Superstructures made by assemblies of metal nanoclusters (NCs) have gained interest due to their atomic precision and exciting photophysical properties. Although there are some reports of cluster-assembled materials of NCs protected with thiols, the preparation of stable thiol-free analogs is largely unexplored due to the poor stability of such structures. Herein, we report the synthesis of phosphine-protected alloy NCs of silver with varying gold doping and superstructures of such systems. We show that alloying of phosphine-protected silver clusters with gold results in comparatively more stable clusters than weakly ligated hydride-and phosphine-coprotected silver clusters. Two new Ag− Au alloy cluster series, [Ag 11−x Au x (DPPB) 5 Cl 5 O 2 ] 2+ , where x = 1− 10 (Ag 11−x Au x in short), and [Ag 15−x Au x (DPPP) 6 Cl 5 ] 2+ , where x = 1−6 (Ag 15−x Au x in short), have been synthesized using two different phosphines, 1,4-bis(diphenylphosphino)butane (DPPB) and 1,3-bis(diphenylphosphino)propane (DPPP), respectively. These alloy clusters possess aggregation-induced emission (AIE) property, which was unexplored till now for phosphine-protected silver clusters. A visibly nonluminescent methanol solution of these clusters showed strong red luminescence in the presence of water due to the formation of cluster-assembled spherical hollow superstructures without any template. A solvophobic effect along with π•••π and C−H•••π interactions in the ligand shell make the alloy NCs assemble compactly within the hollow spheres. The assembly makes them highly emitting due to the restriction of intramolecular motion. The emissive states of the alloy clusters show a many-fold increase in lifetime in the presence of water. Femtosecond transient absorption studies revealed the lifetime of the excited-state charge carriers in their monomeric and aggregated states. Apart from enriching the limited family of phosphine-protected silver alloy NCs, this work also provides a new strategy to build a controlled assembly of NCs with tailored luminescence. These materials could be new phosphors for applications in composites, sensors, thin films, and photonic materials.

This paper examines the determinants of farmers' access to agricultural extension services and adoption of technical inputs. It also attempts to identify what works best for Indian agriculture. Based upon all-India unit-level data of 35,200 farming households surveyed by the National Sample Survey Organisation (NSSO) under the 70 th round in 2013, it applies the binary logistic regression model. The study underlines that the 'Access' to agricultural extension services does not guarantee 'Adoption' of the technologies or better farm practices, as all the variables emerging as significant in case of 'Access' do not emerge as significant for 'Adoption'. The study finds the strong influence of personal and household characteristics on both 'Access' and 'Adoption'. However, socioeconomic and technology variables such as caste, gender, religion, and usage of ICT are found to be important for 'Access' but not for the 'Adoption'. The paper underlines that physical forms of extension services are far more important than the modern ICT driven services in the developing countries like India. It, therefore, recommends significant strengthening of these services with more generous government support.

Active cooling-based atmospheric water generators, despite their growing demand, continue to be energy intensive and offer poor collection efficiencies (energy consumption per liter of water production). Despite progress in micro-/ nanofabrication techniques and functional coatings, advanced surfaces have not been successfully scaled onto such harvesters to accelerate condensation and improve their efficiencies. Here, we present a scalable dualnanostructured hierarchical surface that comprises sporadically distributed bundles of randomly oriented faceted microcones having facets composed of nanostructures, which are either bumps or ridges. Condensate removal on this surface occurs via drop-to-film coalescence, followed by film shedding in the form of macrodrops. Compared to a conventional plain metal surface used for condensation, the improvement in latent heat transfer coefficient using a hierarchically textured surface ranged from 19.9% at a subcooling of ∼8 °C to 1048.4% at a subcooling of ∼1 °C in laboratory scale experiments, subcooling being defined with respect to the dew point. To demonstrate utility at industrial scale and to ensure scalability of the modified surfaces, we create a prototype assembly comprising a tube-fin heat exchanger with hierarchically textured fins, cooled using a standard refrigeration cycle, producing ∼25 L of water per day. The prototype containing hierarchically textured fins provides ∼10.8% enhanced water collection at ∼10.4% improved average collection efficiency compared to the traditional water generator when tested in outdoor conditions.