Clean Water Generation Research Articles

Diatom-Inspired TiO2-PANi-Decorated Bilayer Photothermal Foam for Solar-Driven Clean Water Generation.

Interfacial solar-driven evaporation provides one of the most promising green and sustainable technologies to deal with the knotty water crisis by extracting vapor from a variety of water sources powered by solar energy. Advanced photothermal materials play critical roles in interfacial solar-driven evaporation by photothermal conversion and heat localization. Herein, inspired by the unique hierarchical structure and light-harvesting function of diatoms, we propose a novel photothermal material with a diatom-like hierarchical nanostructure derived from TiO2-PANi-decorated bilayer melamine foam (TiO2-PANi@MF) for solar-driven clean water generation. The diatom-like hierarchical nanostructured TiO2-PANi@MF can realize full-spectrum light absorption and photothermal conversion by enhancing multiple light reflection and light scattering. Thanks to the diatom-like hierarchical nanostructure, TiO2-PANi@MF not only impressively achieves an evaporation rate of 2.12 kg m-2 h-1 under 1 sun irradiation but also shows a high solar steam conversion efficiency up to 88.9%. Notably, the TiO2-PANi composite also endows TiO2-PANi@MF with photocatalytic degradation capability. Apart from the excellent steam generation capability, optimized TiO2-PANi@MF also provides the high photocatalytic efficiency of dye degradation and maintains a high evaporation rate of more than 2 kg m-2 h-1. We believe that the proposed photothermal material with a diatom-like hierarchical nanostructure can envision promising practical applications in seawater desalination and sewage purification.

Sustainable Cellulose Aerogel from Waste Cotton Fabric for High-Performance Solar Steam Generation.

The textile industry has been considered as one of the polluting industries, producing a large amount of textile waste and CO2 emissions each year. Recycling of waste fabric has attracted more research interest in recent years. Herein, renewable polydopamine (PDA)-functionalized cellulose aerogels (CAs) have been designed by a feasible and green way for clean water generation. With the polymerization of PDA on the surface, which possesses excellent photothermal conversion performance and water purification ability, the resulting CA could achieve a high light absorption of 96.5% with the evaporation rate of 2.74 kg m-2 h-1 under 1 sun. Meanwhile, the solar steam generator with the increasing height can absorb energy from adjacent ambient air to strengthen the vapor generation. The features of renewable CAs can achieve efficient water evaporation, which combined with their low material cost and recycling, offer promise in reducing not only energy consumption but also the environmental footprint of cotton textiles.

Intensifying Solar Interfacial Heat Accumulation for Clean Water Generation Excluding Heavy Metal Ions and Oil Emulsions

Solar‐driven interfacial steam generation has emerged as an innovative technique for seawater desalination due to its high photothermal conversion efficiency and potential industrial applications. Herein, a superior interfacial heat accumulation structure composed of semiconductive in situ polymerization (polypyrrole) of nickel foam (IPNF) is reported. The IPNF photothermal layer is assembled with superhydrophilic polyurethane substrate for synchronous water transport and excellent thermal insulation. The 2D ultrablack mesh induces multiple incident rays within the diffused polymerized surface, which allows omnidirectional solar absorption (88.5 %) and intensifying heat localization (49.5 °C @ 1 sun). The state‐of‐the‐art evaporation performances reveal that the integrated IPNF solar evaporator exhibits an excellent evaporation rate (1.74 kg m−2 h−1) and solar‐to‐vapor conversion efficiency (90% excluding heat losses) under 1 kW m−2 solar intensity. Besides this, the long‐term evaporation experiments show negligible discrepancy under seawater conditions (13.27 kg m−2/8 h under 1 kW m−2) and engrain its functioning potential for multimedia and salt rejection (3.2 g × NaCl/240 min). More importantly, herein, insights into different water states in the polymeric network systems during solar‐driven evaporation are provided. This work shows a significant potential to generate freshwater excluding heavy metals and other oil emulsions for industrial applications.

Rapid Catalytic Water Disinfection from Earth Abundant Ca2Fe2O5 Brownmillerite

AbstractWater disinfection is a crucial challenge for humanity. Approaches that are effective, cheap, environmentally friendly, and do not promote gene exchange between bacteria are urgently required. Strongly oxidizing radicals are highly promising to achieve this as they lead to bacterial activation at high efficiencies. However, sources to consistently generate these radicals are limited to high energy UV/H2O2 treatments requiring a large energy input. Here the use of abundant, cheap, brownmillerite (Ca2Fe2O5) is demonstrated as an efficient radical generation material under dark conditions, showing a seven order of magnitude decrease in bacterial concentration over 10 min. This decrease is attributed to the release of interlayer Ca2+ from the layered structure of Ca2Fe2O5 and hydroxyl radical generation. The efficacy of Ca2Fe2O5 is demonstrated by disinfecting turbid sewage sludge. The identification of this cheap, abundant, and nontoxic antibacterial material will provide an opportunity for broad scale clean water generation globally, and address the United Nations’ Sustainable Development Goal of clean water and sanitation.

High‐performance water purification and desalination by solar‐driven interfacial evaporation and photocatalytic VOC decomposition enabled by hierarchical TiO 2 ‐CuO nanoarchitecture

Solar-driven interfacial evaporation for clean water generation has drawn significant attention as a promising and environmentally friendly avenue to tackle the global issue of water scarcity. The collected condensate can be free from most pollutants and impurities of diverse undrinkable water sources, such as heavy metals, organic dyes, minerals, and salts. However, when water is contaminated by volatile organic compounds (VOCs), this approach is ineffective because VOCs also evaporate and even can be enriched in the condensate. Here, we demonstrate TiO2-loaded CuO nanowire-covered Cu foam (TiO2-CuO-Cufoam) for efficient solar-driven interfacial evaporation and synchronous removal of VOCs via photocatalytic degradation. The TiO2-CuO-Cufoam nanoarchitecture possesses high solar absorption, quasi-one-dimensional water pathway, super-hydrophilicity for ultrafast water transport, long-term stability, and potential for cost-effective and scalable production for both VOC removal and desalination, meeting World Health Organization potable water standards. Our TiO2-CuO-Cufoam evaporator simultaneously demonstrates high solar evaporation efficiency of 86.6% and efficiency of 80.0% for the removal of VOCs under one sun (i.e., 1 kW m−2). This result may open new opportunities for energy-efficient, clean water generation from real-world water sources using solar energy. Novelty Statement TiO2-loaded CuO nanowire-covered Cu foam (TiO2-CuO-Cufoam) was obtained through the facile and green synthesis process. The TiO2-CuO-Cufoam nanoarchitecture possesses high solar absorption due to surface nanostructuring, quasi-one-dimensional water pathway for localized thermal management, super-hydrophilicity for ultrafast water transport, TiO2-CuO heterojunction for enhanced photodegradation of VOCs without consumption of chemical reagents, long-term stability, and potential for cost-effective and scalable production. The nanoarchitecture is employed for clean water generation from real-world water sources.

Carbonized rice husk coated solar absorber for clean water generation from seawater with a solar still

ABSTRACT This study demonstrated the generation of clean water from seawater collected at the beach coast in Universiti Malaysia Sabah, Malaysia, with carbonized rice husk coated melamine sponge as solar absorber by a solar still. Melamine sponge was utilized as a seawater transportation medium since its porous structure is excellent in channelling the seawater. Whereas carbonized rice husk was used as the photothermal conversion material for its efficient heat absorption due to its black colour and porous structure. Implementing air gap between the seawater body and solar absorber, and restricted water pathway assisted in localizing heat on the top surface of the solar absorber. Clean water was generated under direct solar radiation during the day at an open space with average solar intensity around 1.1∼1.2 kW/m2 (slightly higher than 1 sun) for about 4 h. Efficiency of the solar absorber was calculated, while the quality of the generated clean water was observed in terms of salinity and pH value. Insulated solar still with carbon-coated sponge showed the highest efficiency at about 54.74%. Salinity of the collected clean water significantly reduced to consumable level which was approximately 55 ppm, and the pH value at about 6.73 where it was within the safe limit of the drinkable water pH.

Naturally Abundant Green Moss for Highly Efficient Solar Thermal Generation of Clean Water.

Water and energy scarcity are the challenges for humankind in the coming years. Sun is the largest source of energy available on the planet. Also, brackish seawater covers more than 70% of the surface of the planet. Therefore, combining these two valuable natural resources represents an appealing solution to overcome the problem of sweet water shortage. To achieve this goal, the missing link is to develop appropriate photothermal materials with efficient light-to-heat-to-vapor generation. In this work, green moss is introduced as a natural, eco-friendly, abundant, superhydrophilic, fast water transporter, salt rejector, and highly efficient solar collector material. Green moss, owing to its open-microgrooves, can supply adequate water to the evaporation surface, while its open capillary channels can reject the precipitated salt, allowing its reusability. The green moss solar steam generator demonstrated an outstanding solar evaporation rate of 2.61 kg m-2 h-1 under 1 sun illumination, which is much higher than other reported natural and chemically modified biomasses under otherwise similar conditions. Interestingly, upon chemical modification of the green moss surface, it is possible to increase its solar evaporation rate to >3 kg m-2 h-1. Using the moss to purify and desalinate brackish water, it was demonstrated that it has the ability to decrease salinity below the WHO standards for drinkable water.

Harvesting Solar Energy by Flowerlike Carbon Cloth Nanocomposites for Simultaneous Generation of Clean Water and Electricity.

Harvesting solar energy for photothermal conversion in an efficient manner for steam-electricity cogeneration is particularly opportune in the context of comprehensive solar utilization to address the challenge of a global shortage of fresh water. However, the fragile solar thermal devices and the single-energy utilization pattern greatly hinder extensive solar energy exploitation and practical application. Herein, a flexible carbon cloth nanocomposite with a biomimetic pelargonium hortorum-petal-like surface that embraces all desirable chemical and physical properties, that is, enhanced light acquisition, excellent photothermal property, and operational durability, for high-performance solar-driven interfacial water evaporation distillation is reported. Combined with the two-dimensional water channel, the solar evaporator shows a solar-to-steam conversion efficiency of 93% under the simulated solar illumination of 1 kW m-2. More strikingly, the solar steam generation-induced electricity based on the practical consideration toward more infusive solar thermal application is proposed. Such integrative steam-electricity generators presented here provide an attractive method to produce on-site electricity and fresh water in an individualized mode in various resource-constrained areas.

Boron nanosheets loaded with MoS2 porous sponges for water purification

Utilizing solar steam generation to treat seawater and sewage, as an emerging and effective technology, can obtain clean water. There is an abundance of water demand and a shortage of water supply in the world today. Herein, we demonstrate an integrated evaporator of boron nanosheets modified with molybdenum disulfide (MoS2) as a photothermal materials and a konjac glucomannan (KGM) sponge with excellent pore structure as a thermal insulator and water supplier for solar clean water generation. A rapid evaporation rate (1.538 kg m−2 h-1) and high solar evaporation efficiency (96.5 %) under 1-sun radiation (1 kW m−2) can be achieved in the two-dimensional structure system. This work provides a new way to design and manufacture renewable solar steam generation for water purification.

Spatial effects of nutrient pollution on drinking water production

According to the U. S. Environmental Protection Agency (USEPA), nutrient pollution was viewed as America’s most “widespread, costly and challenging environmental problem” (USEPA 2020a, https://www.epa.gov/sites/production/files/2015-03/documents/facts_about_nutrient_pollution_what_is_hypoxia.pdf ). The economic damages accruing to nutrient pollution are extensive and substantial. Not only do such “spillovers” affect tourism but also recreational and commercial fishing. Property values are impacted as drinking water is often tapped from aquifers, etc., when groundwater is either not available or its quality has been compromised by the sort of nutrient spillovers we analyze in our paper. The EPA estimates that home prices are up to 25% higher when clean water is available and waterfront property values can decline because of the many problems associated with algal blooms. The costs of treating water that has been polluted from nutrients are substantial. An example is the case of Minnesota where nitrate and algal blooms required nitrate-removal systems that increased the drinking water costs from 5 to 10 cents per 1000 gallons to over $4 per 1000 gallons (USEPA 2020b, https://www.epa.gov/nutrientpollution/effects-economy ). Although the notion that “spillovers” from nutrient pollution exist is intuitive, such externalities have not been evaluated empirically using recent advances in spatial panel econometrics, especially in the context of how such externalities spillover into the supply of drinking water supplied by local water utilities. Such an analysis requires a substantial understanding of how water management decisions are made, the technologies in play, and how various environmental policies, regulations, and directives interact with the generation of clean drinking water when contagion caused by nutrient runoff and poor or illegal pollution abatement strategies by firms pollute our country’s drinking water. Although our study does not formally imbed such factors into a structural model, they do inform our modeling approach and motivate our discussion of sometimes arcane issues surrounding environmental policy, the science of nutrient generation, and how nutrient pollution impacts water quality spatially. Our study explores the spatial effects of nitrogen (N) and phosphorus (P) pollution and drinking water production patterns in agriculture. Two important examples are that water utilities that deliver and treat drinking water in agricultural areas have to deal with excess nitrogen and phosphorus released to the environment by crop and livestock operations, an externality created by the agricultural sector; also, the drinking water production sector in rural areas is highly fragmented, with a multitude of enterprise sizes, organizational forms and network densities that have spatial components. We analyze nutrient pollution based on data collected via the Safe Drinking Water Act of 1974 to estimate how water bodies and sub-basins impaired by nutrient pollution to spatially affect drinking water utilities based on input distance functions that address varying productive efficiencies of water utilities as well as their scale and scope of operations.

Biomass-Derived Carbonaceous Materials with Multichannel Waterways for Solar-Driven Clean Water and Thermoelectric Power Generation

Coping with the shortage of fresh water and electricity in off-grid and resource-constrained areas through sustainable strategies has become the most urgent challenge facing the development of human society. Herein, we propose a low-cost and sustainable way of repurposing discarded pomelo peel by converting it into 3D porous carbon foam (i.e., carbonized pomelo peel, referred to as CPP) with multichannel waterways for synergetic coupling of solar-driven interfacial evaporation (SDIE) and low-grade heat-to-electricity generation. The superhydrophilic 3D porous CPP with multichannel waterways utilizes its powerful water supply capability to avoid salt accumulation during continuous seawater desalination. By cautiously weighing the water transport and thermal management of CPP-based evaporators, CPP with three-channel waterways (CPP3) can achieve efficient solar-driven evaporation (the evaporation rate of 1.37 kg m–2 h–1, one sun) on the premise of salt resistance through its superior light absorption and ultrafast solar-thermal response. Besides, a collaborative device integrating CPP3 and a commercial thermoelectric (TE) generator is designed for synchronous generation of solar steam and thermoelectricity, which can simultaneously achieve an evaporation rate of 1.39 kg m–2 h–1 and a power output of 0.5 W m–2 under one sun illumination. Such a cost-effective and easy-to-manufacture strategy can provide potential opportunities for satisfying the demand for fresh water and electricity in resource-constrained areas.

Clean water generation through a multifunctional activated carbon-TiO2 interfacial solar distillation system.

Solar distillation is emerging as an environmentally friendly and energy-effective technology for clean water generation. However, bulk water heating and the possibly complex composition of water matrices of source water could undermine the system efficacy. In this study, an interfacial evaporation device consisting of activated carbon combined with P25 TiO2 as the top layer and polyethylene foam as the bottom layer (AC-P25/foam device) was established. With the excellent optical absorbance of AC and the heat localization effect contributed by the PE foam, the evaporation rate (revp) of the device (revp = 2.1 kg m−2 h−1) was improved by 209% and 71% compared with that of the water-only (revp = 0.68 kg m−2 h−1) and conventional evaporation (i.e., submerged AC-P25) systems (revp = 1.23 kg m−2 h−1), respectively. The reusability test showed the stable evaporation performance of AC-P25/foam within 7 cycles; this interfacial evaporation was also found to be less affected by suspended solids in water due to a reduction in the influence of light scattering. The AC-P25/foam device not only possessed photothermal ability for water distillation but was also able to prevent enrichment of volatile organic compounds (i.e., phenol) with ∼95% removal efficiency through adsorption and photocatalytic reactions under illumination. Additionally, an outdoor solar distillation test performed with synthetic saline water demonstrated the desalination ability of the AC-P25/foam device, with the concentrations of all ions in the distilled water ≤3.5 mg L−1, far below the drinking water guideline value provided by the World Health Organization. The materials of the AC-P25/foam photothermal device are readily available and easily fabricated, showing the practical feasibility of this device for clean water generation.

Combined antioxidant capped and surface supported redox-sensitive nanoparticles for continuous elimination of multi-metallic species.

A strategic modification involving (i) a multi-functional almond shell biochar surface support and (ii) capping with almond skin extracted antioxidants was performed to preserve redox-sensitive Fe0 nanoparticles (NPs). pXRD data showed generation of an iron-carbonyl shell on the supported Fe0 NPs (SA-Fe0), justifying successful antioxidant capping. The total metal removal capacity of 695 mg g-1i.e. AsO2- (300.2 mg g-1) > Cd2+ (224.2 mg g-1) > CrO42- (125.2 mg g-1) > Ni2+ (44.5 mg g-1) in batch mode, and 102 mg g-1 in continuous column setup confirms the excellent reactivity of the SA-Fe0 nanocomposite. Loss of the iron-carbonyl shell and iron oxidation during interaction with contaminants confirm no hindrance in electron transfer due to antioxidant capping.

Ni‐based Plasmonic/Magnetic Nanostructures as Efficient Light Absorbers for Steam Generation

AbstractSolar steam generation technologies have gained increasing attention due to their great potential for clean water generation with low energy consumption. The rational design of a light absorber that can maximize solar energy utilization is therefore of great importance. Here, the synthesis of Ni@C@SiO2 core–shell nanoparticles as promising light absorbers for steam generation by taking advantage of the plasmonic excitation of Ni nanoparticles, the broadband absorption of carbon, and the protective function and hydrophilic property of silica is reported. The nanoparticle‐based evaporator shows an excellent photothermal efficiency of 91.2%, with an evaporation rate of 1.67 kg m−2 h−1. The performance can be further enhanced by incorporating the nanoparticles into a polyvinyl alcohol hydrogel to make a composite film. In addition, utilizing the magnetic property of the core–shell particles allows the creation of surface texture in the film by applying an external magnetic field, which helps increase surface roughness and further boost the evaporation rate to as high as 2.25 kg m−2 h−1.

All-Day Freshwater Harvesting through Combined Solar-Driven Interfacial Desalination and Passive Radiative Cooling.

Solar-driven interfacial evaporation has received increasing research attention for clean water generation, but freshwater harvesting often occurs only during daytime. Herein, we report a strategy for all-day freshwater harvesting through combining solar-driven interfacial desalination and dew water generation. Through spray-coating carbon nanotubes onto a flexible substrate that has high-infrared emittance in the atmosphere window, a dual functional film was prepared to efficiently absorb solar energy for desalination at daytime and passively cool down the surface temperature to collect dew water at night. By integrating the dual functional film within a three-stage membrane distillation device, the home-made system achieved a drinkable freshwater collection efficiency of 71.1% when desalinating seawater under 1 sun illumination and achieved a dew water collection rate of 0.1 L m-2 day-1 at night. The readily available low-cost raw materials, simple fabrication process of the dual functional films, and the resultant all-day freshwater collection systems make the combined solar-thermal interfacial desalination and dew water collection a promising solution to alleviate the freshwater shortage in many underdeveloped regions, arid areas, and islands.

Multifunctional solar bamboo straw: Multiscale 3D membrane for self-sustained solar-thermal water desalination and purification and thermoelectric waste heat recovery and storage

Solar desalination and purification based on interfacial evaporation have great potential to alleviate global water scarcity. However, real-world interfacial evaporation suffers from several issues in clean water collection and solar-to-clean-water energy efficiency. Here, a new concept of multifunctional natural membrane interfacial evaporation (MNMIE) is demonstrated, achieving the whole cycle of energy conversion from solar energy harvesting to waste heat recovery and storage while effectively desalinating and purifying water. The 3D, multiscale membrane derived from sustainable bamboo presents a mean pore size of 150 nm and a porosity of 63.8%, comparable to the commercial membranes. The as-generated vapor from a self-sustained evaporation process is guided to permeate through the porous bamboo node into the bamboo chamber facing unfocused incident light (1 sun) and then condenses, resulting in a high water collection ratio of 81.0% and solar-to-clean water efficiency of 67.4%. Moreover, the waste heat from desalination is recovered through direct thermoelectric energy conversion and storage under unfocused solar light. The fully integrated cycle of energy conversion, storage, and utilization for clean water and electricity generation enabled by the multifunctional natural membrane is scalable, economic and represents a highly promising solution for sustainable energy cycles enabled by nanotechnology-empowered natural resources.

Banyan-inspired hierarchical evaporators for efficient solar photothermal conversion

As a direct approach to utilize the abundant solar energy, solar steam generation surges in recent decade to generate fresh water from sewage and seawater, while still suffering from challenges like a limited photothermal efficiency and scale manufacturing. To enhance the solar energy utilization efficiency, inspired from banyan tree, we demonstrate a new, scalable and low-cost hierarchical evaporator, comprising an activated carbon-cotton fabric as photothermal leaves, commercial polyester pillars as prop roots, and expandable polyethylene foams, to largely utilize solar energy. The both sides of fabric and lateral area of polyester pillars collectively contribute to a rather high evaporation rate 1.95 kg m−2 h−1, with enhanced solar efficiency under 1 sun illumination. Polyester pillars as water paths can reduce the contact area between the photothermal layer and bulk water to prevent heat loss. The hierarchical evaporator is able to enhance solar energy utilization by increasing the extra evaporation area including the bottom side of fabric and lateral area of polyester pillars and thus behave most similarly to the transpiration process of banyan tree from both sides of leaves and prop roots. Moreover, the proposed hierarchical evaporator is further demonstrated to possess anti-salt-clogging performance by changing the number of polyester pillars. The banyan-inspired hierarchical evaporator is scalable, feasible, and low-cost, showing great potential for direct industrial applications of solar energy on clean water generation and sewage treatment.

Effect of folding on 3D photothermal cones with efficient solar-driven water evaporation

Efficient management of solar irradiation into exploitable thermal energy for fast generation of clean water has been the recent focus. However, the solar-driven evaporation is generally limited to the unidirectional evaporation, and the production rate is still low and further efforts are still required in order to enhance light harvesting and evaporation efficiency. Polypyrrole (PPy) was previously coated on polymer cone to demonstrate its superior light absorption and conversion caused by the multiple reflections of incident light inside the cone’s cavity. Instead of plane polymer cone, folded cones made of inexpensive, ready-available filter paper were used in this study to prove the effect of increasing folds in enhancing the light absorbance and heat conversion. As fold increases the reflection area inside the cone, the light-to-heat and the solar conversion efficiency are therefore increased with the increase of fold on the paper cones. The solar conversion efficiency of the cone with 32 folds reached 83.9% under one sun illumination, which is higher than the plane cone. Practical application of desalination of the folded cone also was demonstrated in this study. Based on the present result, 3D structure of the photothermal material is important in controlling final performance of the solar-driven water evaporation device and the idea of using folded structure can be applied to other photothermal materials, thus providing foundation for developing novel solar-driven water evaporation device.

Clean Water from Air Utilizing Black TiO2-Based Photothermal Nanocomposite Sheets

Herein, we demonstrate a simple, highly efficient, and cost-effective clean water generation strategy that can be implemented in the geographical locations deprived of freshwater resources. We capt...

Biomass-derived porous carbon for excellent low intensity solar steam generation and seawater desalination

In recent times, solar-driven desalination has emerged as a sustainable solution for the impending water crisis. Herein, we report a novel solar-driven steam generator manufactured from porous carbon derived from sweet lime peels (a food waste) and polyvinyl alcohol sponge for efficient steam generation and its application in solar seawater desalination. The solar steam generator fabricated with a unidirectional pathway design satisfactorily absorbed incoming solar illumination, provided localized heat at the air-water interface and produced steam at a rate of 1.386 kg m−2 h−1, exhibiting an excellent photothermal efficiency of 90.88% under 1 sun (1000 W m−2) illumination. Furthermore, the steam generator proved capable of maintaining its performance in lower solar intensities (<1 sun), making it an excellent device for seawater desalination. Bearing in mind the aforementioned virtues, the steam generator was incorporated into a facile laboratory solar still for passive solar desalination. The modified solar still could generate clean water even at low simulated solar intensities with a near-100% salt removal efficiency. Moreover, the excellent performance of the solar still was retained in long-term and real-life experimentation and resulted in sustained clean water generation. The merits of the solar still, such as facile fabrication technique, low cost, scalability, and excellent desalination performance should inspire further research in solar steam generator-based solar stills for solar seawater desalination.