Xie Zeng

Bio: Xie Zeng is an academic researcher from University at Buffalo. The author has contributed to research in topics: Plasmon & Metamaterial. The author has an hindex of 17, co-authored 65 publications receiving 1564 citations. Previous affiliations of Xie Zeng include Fudan University & State University of New York System.

Extremely Cost‐Effective and Efficient Solar Vapor Generation under Nonconcentrated Illumination Using Thermally Isolated Black Paper

Abstract: Passive solar vapor generation represents a promising and environmentally benign method of water purification/desalination. However, conventional solar steam generation techniques usually rely on costly and cumbersome optical concentration systems and have relatively low efficiency due to bulk heating of the entire liquid volume. Here, an efficient strategy using extremely low-cost materials, i.e., carbon black (powder), hydrophilic porous paper, and expanded polystyrene foam is reported. Due to the excellent thermal insulation between the surface liquid and the bulk volume of the water and the suppressed radiative and convective losses from the absorber surface to the adjacent heated vapor, a record thermal efficiency of ≈88% is obtained under 1 sun without concentration, corresponding to the evaporation rate of 1.28 kg (m2 h)-1. When scaled up to a 100 cm2 array in a portable solar water still system and placed in an outdoor environment, the freshwater generation rate is 2.4 times of that of a leading commercial product. By simultaneously addressing both the need for high-efficiency operation as well as production cost limitations, this system can provide an approach for individuals to purify water for personal needs, which is particularly suitable for undeveloped regions with limited/no access to electricity.

Dielectric-Grating-Coupled Surface Plasmon Resonance From the Back Side of the Metal Film for Ultrasensitive Sensing

Abstract: We propose a dielectric grating that can launch surface plasmon resonance (SPR) modes efficiently on the other side of flat metal films, which is similar to the conventional prism coupling mechanism. Importantly, this structure can excite SPR under the normal incident light, which is particularly suitable for the integration with optical fiber tips. By launching the SPR mode near the wavelength of 1.55 $\mu\text{m}$ with a very narrow resonance line width (∼4 nm), this structure is promising for the development of high-performance portable, flexible, and real-time refractometric sensing applications.

Cold Vapor Generation beyond the Input Solar Energy Limit.

Abstract: 100% efficiency is the ultimate goal for all energy harvesting and conversion applications. However, no energy conversion process is reported to reach this ideal limit before. Here, an example with near perfect energy conversion efficiency in the process of solar vapor generation below room temperature is reported. Remarkably, when the operational temperature of the system is below that of the surroundings (i.e., under low density solar illumination), the total vapor generation rate is higher than the upper limit that can be produced by the input solar energy because of extra energy taken from the warmer environment. Experimental results are provided to validate this intriguing strategy under 1 sun illumination. The best measured rate is ≈2.20 kg m-2 h-1 under 1 sun illumination, well beyond its corresponding upper limit of 1.68 kg m-2 h-1 and is even faster than the one reported by other systems under 2 sun illumination.

Rainbow Trapping in Hyperbolic Metamaterial Waveguide

Abstract: The recent reported trapped "rainbow" storage of light using metamaterials and plasmonic graded surface gratings has generated considerable interest for on-chip slow light. The potential for controlling the velocity of broadband light in guided photonic structures opens up tremendous opportunities to manipulate light for optical modulation, switching, communication and light-matter interactions. However, previously reported designs for rainbow trapping are generally constrained by inherent difficulties resulting in the limited experimental realization of this intriguing effect. Here we propose a hyperbolic metamaterial structure to realize a highly efficient rainbow trapping effect, which, importantly, is not limited by those severe theoretical constraints required in previously reported insulator-negative-index-insulator, insulator-metal-insulator and metal-insulator-metal waveguide tapers, and therefore representing a significant promise to realize the rainbow trapping structure practically.

Broadband absorption engineering of hyperbolic metafilm patterns

Abstract: Perfect absorbers are important optical/thermal components required by a variety of applications, including photon/thermal-harvesting, thermal energy recycling, and vacuum heat liberation. While there is great interest in achieving highly absorptive materials exhibiting large broadband absorption using optically thick, micro-structured materials, it is still challenging to realize ultra-compact subwavelength absorber for on-chip optical/thermal energy applications. Here we report the experimental realization of an on-chip broadband super absorber structure based on hyperbolic metamaterial waveguide taper array with strong and tunable absorption profile from near-infrared to mid-infrared spectral region. The ability to efficiently produce broadband, highly confined and localized optical fields on a chip is expected to create new regimes of optical/thermal physics, which holds promise for impacting a broad range of energy technologies ranging from photovoltaics, to thin-film thermal absorbers/emitters, to optical-chemical energy harvesting.

Highly efficient solar vapour generation via hierarchically nanostructured gels

Abstract: Solar vapour generation is an efficient way of harvesting solar energy for the purification of polluted or saline water. However, water evaporation suffers from either inefficient utilization of solar energy or relies on complex and expensive light-concentration accessories. Here, we demonstrate a hierarchically nanostructured gel (HNG) based on polyvinyl alcohol (PVA) and polypyrrole (PPy) that serves as an independent solar vapour generator. The converted energy can be utilized in situ to power the vaporization of water contained in the molecular meshes of the PVA network, where water evaporation is facilitated by the skeleton of the hydrogel. A floating HNG sample evaporated water with a record high rate of 3.2 kg m−2 h−1 via 94% solar energy from 1 sun irradiation, and 18–23 litres of water per square metre of HNG was delivered daily when purifying brine water. These values were achievable due to the reduced latent heat of water evaporation in the molecular mesh under natural sunlight. Effective energy confinement via tailored water transport in hierarchical nanostructured gels enables highly efficient solar vapour generation.

Solar-driven interfacial evaporation

Abstract: As a ubiquitous solar-thermal energy conversion process, solar-driven evaporation has attracted tremendous research attention owing to its high conversion efficiency of solar energy and transformative industrial potential. In recent years, solar-driven interfacial evaporation by localization of solar-thermal energy conversion to the air/liquid interface has been proposed as a promising alternative to conventional bulk heating-based evaporation, potentially reducing thermal losses and improving energy conversion efficiency. In this Review, we discuss the development of the key components for achieving high-performance evaporation, including solar absorbers, evaporation structures, thermal insulators and thermal concentrators, and discuss how they improve the performance of the solar-driven interfacial evaporation system. We describe the possibilities for applying this efficient solar-driven interfacial evaporation process for energy conversion applications. The exciting opportunities and challenges in both fundamental research and practical implementation of the solar-driven interfacial evaporation process are also discussed. The thermal properties of solar energy can be exploited for many applications, including evaporation. Tao et al. review recent developments in the field of solar-driven interfacial evaporation, which have enabled higher-performance structures by localizing energy conversion to the air/liquid interface.

Solar absorber material and system designs for photothermal water vaporization towards clean water and energy production

Abstract: Photothermal materials with broad solar absorption and high conversion efficiency have recently attracted significant interest. They are becoming a fast-growing research focus in the area of solar-driven vaporization for clean water production. The parallel development of thermal management strategies through both material and system designs has further improved the overall efficiency of solar vaporization. Collectively, this green solar-driven water vaporization technology has regained attention as a sustainable solution for water scarcity. In this review, we will report the recent progress in solar absorber material design based on various photothermal conversion mechanisms, evaluate the prerequisites in terms of optical, thermal and wetting properties for efficient solar-driven water vaporization, classify the systems based on different photothermal evaporation configurations and discuss other correlated applications in the areas of desalination, water purification and energy generation. This article aims to provide a comprehensive review on the current development in efficient photothermal evaporation, and suggest directions to further enhance its overall efficiency through the judicious choice of materials and system designs, while synchronously capitalizing waste energy to realize concurrent clean water and energy production.