Xiuping Zhu

Charged hydrogels can swell in salty water, while a portion of salt ions are repelled by the fixed charged groups in the hydrogels. This characteristic of charged hydrogels grants them with excellent potential for desalination. Attributed to their high osmotic pressure, hydrogels can absorb large amounts of water. Conversely, when a swollen hydrogel is exposed to an environment with higher osmotic pressure, it releases absorbed water, yielding comparatively dilute product water. In this study, ammonium bicarbonate (NH4HCO3), which can be regenerated and recycled by waste heat, was introduced to provide high osmotic pressure to dewater swollen poly (acrylic acid-co-acrylamide) (PAAM) hydrogels. A water recovery of nearly 48 % and a salt rejection of 58 % were obtained for 0.85 g/L NaCl solutions. Even in real well water (~1.3 g/L NaCl), the hydrogel-NH4HCO3 system recovered 43 % of water and rejected …

Hydrogels possess a strong water absorption capability and can release absorbed water in response to physical or chemical stimuli, making them promising materials for water recycling. To explore the concept of using hydrogels to recover water from wastewater, we synthesized and utilized poly(acrylic acid-co-acrylamide) (PAAM) hydrogels to extract water from solutions containing various organic pollutants and salt concentrations. The swelling ratio of PAAM hydrogels reached up to 510 g/g with a water recovery of around 44% and a water production rate of approximately 3200 L/kg/day. The removal rates of organic pollutants reached up to 89%, depending on the pollutant’s properties such as molecular weight, functional group, solubility, and charge. This confirms the potential of using hydrogels to recover water from various wastewaters, especially for those containing large molecular pollutants.

The world is facing severe environmental pollution and energy shortages. Microbial electrolysis cells (MECs) provide a promising solution by producing H2 from wastewater. However, MECs face limitations, such as low current densities, slow H2 production, and electrogenic bacteria deactivation at high voltages. In this study, we developed microbial water electrolysis cells (MWECs), a new device that couples MECs with water electrolysis (WE). At an applied voltage of 2.2 V, MWECs achieved an industrial-level high current density of 400 mA/cm2, a fast H2 production rate of 121 L-H2/L/d, and a low energy consumption of 5.93 kWh/m3. Moreover, the protective effect of the abiotic anode in water electrolysis enabled microorganisms to maintain robust activity at high voltages in MWECs, with Geobacter, Azospirillum, and Paracoccus as the dominant genera. This led to a 2-fold increase in chemical oxygen demand …

The global problem of petroleum contamination in soils seriously threatens environmental safety and human health. Current studies have successfully demonstrated the feasibility of bioelectrokinetic and bioelectrochemical remediation of petroleum-contaminated soils due to their easy implementation, environmental benignity, and enhanced removal efficiency compared to bioremediation. This paper reviewed recent progress and development associated with bioelectrokinetic and bioelectrochemical remediation of petroleum-contaminated soils. The working principles, removal efficiencies, affecting factors, and constraints of the two technologies were thoroughly summarized and discussed. The potentials, challenges, and future perspectives were also deliberated to shed light on how to overcome the barriers and realize widespread implementation on large scales of these two technologies.

This chapter is devoted to special heat engines. It is a broad group that includes salinity gradient heat engine technologies of different nature and that cannot be included within the classes of osmotic heat engines and reverse electrodialysis heat engines.The chapter is divided into three different parts, each one presenting the latest achievements and development of a specific heat engine: (Part 1) accumulator mixing (ACCMIX) technologies and relevant perspectives, (Part 2) fundamentals and state of the art of thermally regenerative ammonia battery (TRAB), and (Part 3) fundamentals of hydrogels and their applications in salinity gradient heat engines.

Hydrogels can be employed to recover salinity gradient (SG) energy as they can exhibit reversible swelling and shrinking behaviors in alternate freshwater and sea water. The swelling ratio and mechanic property of hydrogels are essential for the SG energy harvest. Herein, different amounts of graphene oxide (GO) or carbon nanotube (CNT) were successfully introduced to the matrix of poly(acrylic acid-co-acrylamide) (PAAM) hydrogels. Compared to the original PAAM hydrogels, both the swelling property and mechanic strength of the GO/CNT hybrid PAAM hydrogels were significantly enhanced. Although the CNT/PAAM hydrogels exhibited relatively higher swelling ratio (1578 g g−1) than that of GO/PAAM (1423 g g−1), the highest SG energy recovery was obtained by using GO/PAAM hydrogels (7.07 J g−1). The reason was due to the better mechanical strength of GO/PAAM hydrogels, which resulted from the …

Fe(II)-catalyzed ferrihydrite transformation under anoxic conditions has been intensively studied, while such mechanisms are insufficient to be applied in oxic environments with depleted Fe(II). Here, we investigated expanded pathways of sunlight-driven ferrihydrite transformation in the presence of dissolved oxygen, without initial addition of dissolved Fe(II). We found that sunlight significantly facilitated the transformation of ferrihydrite to goethite compared to that under dark conditions. Redox active species (hole–electron pairs, reactive radicals, and Fe(II)) were produced from the ferrihydrite interface via the photoinduced electron transfer processes. Experiments with systematically varied wet chemistry conditions probed the relative contributions of three pathways for the production of hydroxyl radicals: (1) oxidation of water (5.0%); (2) reduction of dissolved oxygen (40.9%); and (3) photolysis of Fe(III)-hydroxyl …

Microbial photoelectrochemical systems (MPECs) is promising for sustainable energy and resources recovery from wastewater, however, the synergistic effects between the photoelectrode and bioelectrode remain unclear. In this study, a hybrid MPEC configurated with a Fe2O3 photo-bioanode and a black-silicon (b-Si) photocathode was proposed for sustainable electricity and H2 production from wastewater. The dual photoelectrodes utilized solar light to generate photoelectrons and holes with enhanced light absorption. Mixed-culture biofilm formed on the photo-bioanode generated electrons and protons from wastewater.. Photoelectrons were transferred from the photoanode to the bioanode, and later arrived at the photocathode for electricity and H2 production. The electrons transfer mechanisms were studied under different irradiation conditions. The system achieved a maximum current density of 0.8 mA/cm2 …

Massive amounts of low-grade thermal energy (<120°C) globally exists in various industrial production processes (i.e., power plants and glass production), nature (i.e., geothermal and solar energy) and living organisms (i.e., human body), and it is gradually recognized as a potential renewable energy resource, and the increasing energy crisis and environmental problems can be alleviated by the help of converting it into electrical energy efficiently. In recent ten years, a variety of liquid-based heat-to-electricity systems or batteries have been proposed and have realized the conversion of low-grade thermal energy to electrical energy or mechanical work with lower material costs and high efficiency and power density. Among them, bimetallic thermally-regenerative ammonia batteries (B-TRABs) have gained much higher power density (the power densities of Cu/Zn-TRAB and Ag/Zn-TRAB are more than 500 Wm-2 …

Development of effective, environmentally friendly, facile large-scale processing, and low-cost materials is critical for renewable energy production. Here, MnOx/biochar composites were synthesized by a simple pyrolysis method and showed high performance for salinity gradient (SG) energy harvest in concentration flow cells (CFCs). The peak power density of CFCs with MnOx/biochar electrodes was up to 5.67 W m–2 (ave. = 0.91 W m–2) and stabilized for 500 cycles when using 1 and 30 g L–1 NaCl, which was attributed to their high specific capacitances and low electrode resistances. This power output was higher than all other reported MnO2 electrodes for SG energy harvest due to the synergistic effects between MnOx and biochar. When using a mixture with a molar fraction of 90% NaCl and 10% KCl (or Na2SO4, MgCl2, MgSO4, and CaCl2) in both feed solutions, the peak power density decreased by 2.3–40 …

An enormous source of clean energy, called salinity gradient (SG) energy, exists from mixing waters with different salinities. Harvesting SG energy has attracted lots of attentions to develop efficient technologies. However, the power output is still limited. In this study, a concentration flow cell (CFC) powered by a bioelectrochemical system, defined as a bio-CFC, was proposed to recover SG energy from synthetic seawater (30 g/L NaCl) and river water (1 g/L NaCl) efficiently. The maximum power density of the bio-CFC reached 42 ± 2 W/m2, which was three times higher than that of a single CFC (10.6 ± 0.1 W/m2). The significant improvement was attributed to the additionally developed capacitive potential, which was formed by the bioelectrochemical currents from degradation of the organics in wastewater. The capacitive potential enhanced the Na+ intercalation/deintercalation on the electrodes and accelerated the …

Bimetallic thermally-regenerative ammonia batteries (B-TRABs) exhibit great potential in converting low-grade waste heat into electricity due to their high power and energy densities. However, there are still key issues such as self-discharge, low anode coulombic efficiency (ACE), and side reactions in ammonia batteries, which are not well explained but have a significant impact on performance. Here, we focus on the electrode reaction mechanism and give a universal construction criterion for the bimetallic thermally-regenerative batteries. The influence of oxygen on the electrode reactions of each process is explored, and a flow Cu/Zn-TRAB is developed to verify the electrochemical analysis. The root cause for affecting the ACE and oxygen effect are examined. The generation of self-discharge and its different effects are investigated for each electrode process. In addition, the influence of initial catholyte pH and …

Hydrogels came into light with the first synthetic hydrogels established in 1954 [1, 2]. They are polymeric materials with cross-linked, three dimensional (3D) hydrophilic network structures which can absorb and retain a significant volume of water in their reticulated structures, thereby exhibiting swelling/shrinking behavior [3, 4]. The polymeric network of hydrogels is formed by the cross-linking of homopolymers or copolymers via physical/chemical interactions [5]. Physical cross-linking includes hydrogen bonding, electrostatic interactions, or hydrophobic interactions between polar groups, which are all temporal connections. On the other hand, chemical cross-linking is a permanent connection formed by covalent bonds or the ionic connection between various functional groups, which introduced by the cross-linking agents [6]. The capacity of hydrogels to hold water relies on the presence of a large number of hydrophilic groups such as dOH, dCONH2, dCONHd, dCOOH, and dSO3H in the polymeric chains [6]. The presence and dissociation of these ionic species within the network of hydrogels are responsible to swell and develop a higher internal osmotic pressure. The swelling pressure (Π) of hydrogels originates from osmotic pressures of ionizable groups (Π ion), elastic reaction forces of the network (Πel), and the polymer-water mixing (Π mix)[7–9]:

Wastewaters contain abundant nutrients and energy, which can be recovered by using proper bioelectrochemical systems. We developed a three-chamber resource recovery microbial fuel cell (RRMFC) to treat synthetic urine-containing wastewater with various organic pollutants and simultaneously recover nutrients (e.g., N, P, and S). Over one cycle (∼3 days), 99% of urea, 97% of COD, 99% of histidine, 91% of creatinine, 99% of sodium acetate, 98% of SO4 2−, and 99% of PO4 3− were removed from the wastewater, and simultaneously 42% of total nitrogen, 37% of PO4 3−, 59% of SO4 2−, and 33% of total salts were recovered from the wastewater. We also developed a solar microbial electrolysis cell (solar-MEC) with a Fe2O3 photoanode, a bioanode, and a black-silicon (b-Si) photocathode for H2 production from wastewater without external bias. The solar-MEC had a …

The bimetallic thermally-regenerative ammonia flow battery (B-TRAFB) has exhibited good potential in harvesting low-grade waste heat as high-power electricity, mainly due to its feature of high-voltage discharge and low-voltage charge in room temperature. Here, a 2-D flow and electrochemical coupled model is firstly constructed for a Cu/Zn-TRAFB, and validated with experimental results. We mainly focus on analysis of the influence of different working conditions and reactant concentrations on power and energy densities and thermoelectric conversion efficiency, as well as how the concentration distribution affects the battery performance. The results show that at low power output (~13 W m−2), the highest efficiency of 12.8% (81% relative to Carnot efficiency) can be achieved with an energy density of 17 kW h m−3 and a reactant concentration of 0.3 M. When generating ~70% of the peak power (~175 W m−2 …

The treatment of heavy metal ions in wastewater is of great significance for protecting the environment and human health. To improve the power density and removal efficiency of thermally regenerative ammonia electro-deposition battery and expand the concentration range of effective wastewater removal, a new method for removing Cu(II), Co(II), Ni(II) and Ag(I) from wastewater while generating high-power electric energy by using waste heat, called bimetallic thermally regenerative electro-deposition battery (B-TREB), was constructed in this work. For Cu(II)-containing wastewater with a wide concentration range of 0.002–0.3 M, the removal efficiency (RE) of Cu/Zn-TREB could reach more than 90%. With the initial concentration of Cu(II) being increased from 0.0005 to 0.3 M, the peak power density was enhanced from 20 to 546 W m−2. Besides, for 0.01 M and 0.1 M Co(II) wastewaters, the REs of Co/Zn …

Polymer technologies, such as polymeric flocculants and ion exchange resin, have been widely used in the field of environmental science and engineering. During the past several decades, more damages to human health or ecosystem services have been linked to environmental contamination. It is essential to detect environmental contaminants and mitigate the toxic effects to human or ecosystem receipts. However, many environmental contaminants are persistent and recalcitrant to decomposition in the natural environment or conventional engineered approaches. erefore, advanced polymer technology has become an attractive choice for detection and elimination of emerging pollutants. e purpose of this special issue is to provide the frontiers into the development and application of various polymer technologies for quantification and removal of these contaminants, such as biodegradable polymer materials and polymeric metal-organic frameworks and so on. All accepted papers are summarized as follows. e paper by R. Gong et al. evaluated the effects of diethylhexyl phthalate (DEHP), a common plasticizer in industrial production, on the anaerobic fermentation process in waste activated sludge. e results revealed that DEHP primarily inhibited the solubilizationof protein and polysaccharide in the anaerobic fermentation system, but demonstrated no apparent effects on other processes. e presence of DEHP reduced the abundance of acetogen bacteria and increased the abundance of methanogens. However, no observed changes in the diversity of microbial communities, as well as the total yield and composition of short-chain fatty acids are …

Thermally regenerative ammonia batteries (TRABs) show viable potential for harvesting abundant low-grade waste heat as high-power electricity. However, the ammonia brings about a large pH difference between the catholyte and anolyte, leading to self-discharge and severe energy decay. Here, an electrolyte decoupling strategy is proposed for ammonia batteries to restrain the self-discharge and enhance energy density as well as power generation at high temperatures. The self-discharge by ion cross contamination is observed visually as a colour evolution of the interlayer solution, and a transition of the principal cathodic reactant from Cu2+ to Cu(NH3)42+ exists during discharging, which signals the beginning of performance degradation. The results demonstrate that decoupled Cu/Zn-TRABs with double and triple-membrane designs improve the energy density by 45–50%, mainly due to the delay of the …

Residues and distribution of neonicotinoid insecticides (NEOs) in soil-water-sediment systems of the urban and rural areas of Guangzhou, South China were investigated. A total of 104 soil samples from 7 different functional zones and 29 water/sediment samples from creeks were collected. The results showed that at least one neonicotinoid insecticide was detected in all samples. The summed levels of five target neonicotinoids (∑5neonics) were in the range of 0.003–229 ng/g dw for soil samples, 7.94–636 ng/L for water samples, and 0.017–31.3 ng/g dw for sediment samples, with a geometric mean of 0.59 ng/g dw, 153 ng/L and 1.11 ng/g dw, respectively. Soils from agricultural areas contained the highest residual NEOs, followed by commercial, traffic, residential, industrial, educational zones and parks. Among the seven different functional zones studied, imidacloprid was the most dominant NEO in the …

Salinity gradient (SG) energy is a large untapped energy source available worldwide. Here we applied MoS2 with tunable interlayer spacing to a concentration flow cell for efficient SG energy recovery. By expanding the interlayer from 0.63 nm to 0.96 nm, the ion diffusion resistance was significantly reduced and the pseudocapacitance was largely promoted. These enhanced electrochemical properties resulted in a superior performance of the concentration flow cell on SG energy extraction. The cell with interlayer-expanded MoS2 electrodes produced 11 times of the average power density compared with the cell with original MoS2 electrodes when using model seawater and river water solutions. The interlayer-expanded MoS2 was also among the most durable materials for SG energy harvesting as it allowed the cell to run over 120 cycles and work efficiently at varying salinity concentrations. When provided with …