Waterproof Phase Change Material with a Facilely Incorporated Cellulose Nanocrystal/Poly(N-isopropylacrylamide) Network for All-Weather Outdoor Thermal Energy Storage.

The incorporation of porous supporting materials to prepare shape-stable phase change materials (PCMs) is of great interest in recent years. However, extensive reported composite PCMs are shape-stable in the air atmosphere but neglected in the water environment. To develop shape-stable and waterproof PCMs is important for their outdoor applications but challenging. Herein, we report a novel cellulose nanocrystal/poly(N-isopropylacrylamide) (CNC/PNIPAM) gel-supported hexadecanol (H-anol) PCM with good thermal storage properties and excellent shape stability in both air and water environments. The CNC/PNIPAM hydrogel is prepared through an ultraviolet-induced C═C cross-linking reaction, and its physical structure and mechanical properties are well characterized. H-anol is then directly immerged into the CNC/PNIPAM alcogel by a facile and low-cost solvent-exchange strategy. The mechanism of the solvent-exchange strategy has been established. Because of the temperature-sensitive hydrophilic/hydrophobic transform behavior of the CNC/PNIPAM network, the CNC/PNIPAM/H-anol PCM displays excellent shape stability in a water environment by forming a dense hydrophobic surface, providing it with great potential in all-weather thermal energy storage applications.

[Change of extreme chilling and its impact on winter planting in Guangdong Province, China]. / å¹¿ä¸œçœå¯’å®³æžå€¼å˜åŒ–åŠå ¶å¯¹å†¬ç§ç”Ÿäº§çš„å½±å“.

Based on daily temperature data of 86 weather stations during winter producing season from 1961 to 2017 in Guangdong Province, the temporal and spatial distribution of extreme chilling was analyzed. The return periods of extreme chilling at county level were calculated with the theory of generalized extreme value distribution to provide technical support for extreme chilling risk assessment and early warning together with real-time meteorological disaster prevention and mitigation in winter planting areas. Results showed that there was a general downward trend of the extreme values of chilling accumulation in main winter planting zones. Zhanjiang and Meizhou had declined significantly since the mid-1980s, while Maoming, Shaoguan and Guangzhou had declined significantly since the 21st century. The extreme minimum temperature followed a curve trending generally downward first and upward later on, with a significant rising in Shaoguan from later 1980s while a descending in Guangzhou in the last five years. The order of the number of extreme value stations of chilling accumulation was 1970s ＞ the 21st century ＞ 1990s ＞ 1960s ＞ 1980s. The order of the number of stations of extreme minimum temperature was 1960s ＞ 1990s ＞ the 21st century ＞ 1970s ＞ 1980s. The theoretical forecast values of cold disaster of 2, 5, 10, 20, 50, and 100 year return period showed obvious zonal distribution characteristics. The chilling accumulation diminished from the north to the south and the extreme minimum temperature was higher in the south and lower in the north, which was consistent with the distribution trend in the actual occurrence of cold damage. Typical cases showed more extended chilling return periods in the south than in the north. In Zhanjiang and Maoming, the main producing areas of winter crops in Guangdong Province, the return period of cold damage was long, the probability of extreme cold damage was small but the damage was heavy, and the area of winter crops was in the front rank, which should be paid attention. Our results could provide scientific reference for local government and relevant departments in Guangdong Province to guide winter planting and develop countermeasures against climate change.

Flexible Anti-Biofouling MXene/Cellulose Fibrous Membrane for Sustainable Solar-Driven Water Purification.

Solar-driven interfacial water evaporation is regarded as an effective, renewable, and environment-friendly technology for clean water production. However, biofouling caused by the nonspecific interaction between the steam generator and biofoulants generally hinders the efficient application of wastewater treatment. Herein, this work reports a facile strategy to fabricate flexible anti-biofouling fibrous photothermal membrane consisting of a MXene-coated cellulose membrane for highly efficient solar-driven water steam evaporation toward water purification applications. The as-prepared MXene/cellulose photothermal membrane exhibits light absorption efficiency as high as ∼94% in a wide solar spectrum range and a water evaporation rate up to 1.44 kg m-2 h-1 under one solar illumination. Also, the MXene/cellulose membrane shows very high antibacterial efficiency (above 99.9%) owing to the MXene coating as a highly effective bacteriostatic agent. Such a flexible, anti-biofouling, and high-efficiency photothermal membrane sheds light on practical applications in long-term wastewater treatments.

Human Skin-Inspired Electronic Sensor Skin with Electromagnetic Interference Shielding for the Sensation and Protection of Wearable Electronics.

Increasingly serious electromagnetic radiation pollution puts higher demands on wearable devices. Electronic sensor skin capable of shielding electromagnetic radiation can provide extra protection in emerging fields such as electronic skins, robotics, and artificial intelligence, but combining the sensation and electromagnetic shielding performance together remains a great challenge. Here, inspired by the structure and functions of the human skin, a multifunctional electronic skin (M-E-skin) with both tactile sensing and electromagnetic radiation shielding functions is proposed. The tactile sensing of human skin is mimicked with irregular dermislike rough surfaces, and the electromagnetic shielding performance not available on natural skin is introduced by mimicking the ultraviolet electromagnetic radiation absorption of melanin in epidermis. The M-E-skin shows superior sensitivity (9.8 × 104 kPa-1 for the pressure range 0-0.2 kPa and 3.5 × 103 kPa-1 within 0.2-20 kPa), broad operating range (0-20 kPa), fast response and relaxation times (<62.5 ms), great pressuring-relaxing stability (10 kPa, 1000 cycles), low operating voltage (0.1 V), low power consumption (1.5 nW), and low detection limit (5 Pa). Besides, a broad range of electromagnetic wave (0.5-7.5 GHz) is shielded more than 99.66% by the M-E-skin. This work holds great potential to enlarge the application scope of current electronic skins.

Tannic acid functionalized graphene hydrogel for organic dye adsorption.

Water purification provides a feasible way to relieve the pressure of water shortage and water pollution which we are facing and adsorption is one of the most effective ways to turn polluted water into clean water. Here, we prepared graphene-tannic acid hydrogel using graphene oxide and tannic acid, a natural green reducer and adsorbent, through one-step hydrothermal method. The composition, structure, and morphology of the compounds were systematically examined. The adsorption of dyes was mainly influenced by the morphology and chemical properties of gel. The addition of tannic acid, a molecule rich in oxygen containing functional groups, changed the surface chemistry of graphene sheets and microstructures of gels, which was beneficial for contaminate adsorption. Compared with reduced graphene oxide hydrogel, the graphene-tannic acid hydrogel showed an outstanding adsorption capacity for organic dye methylene blue, more than 500 mg/g at pH 10 and the maximum adsorption capacity was up to 714 mg/g. After adsorption, ethanol and inorganic acid solution can be used as desorption agent and there was no significant adsorption capacity loss after 5 cycles.

[Application of extreme value distribution theory in the forecast of chilling return periods of Guangdong Province, China.] / 极值分布理论在广东寒害重现期预测中的应用.

Chilling is the third weather disaster following flood and typhoon in Guangdong Province. Prediction of chilling return period is of practical significance for scientific reduction and protection of disaster. Four models, including Gumbel distribution, Weibull distribution, log-normal distribution and Peasron-III distribution, were applied, based on the chilling index, to fit the probability distribution of chilling extreme calculated by chilling accumulation for 86 weather stations of Guangdong Province from 1961 to 2015 (December to the following February). The optimal models were selected to calculate the chilling extreme value of return periods. Results showed that Pearson-III distribution was the optimal model for 77 out of the 86 weather stations. The log-normal distribution was optimal for eight weather stations and Gumbel distribution was optimal for only one station. Weibull distribution was not suitable for modeling extreme value of Guangdong Province. Different return periods of 10-, 25-, 50- and 100-year were predicted by optimal distribution models respectively, with a relative error less than 6%. Chilling extreme for years presented obviously latitude distribution feature, with more in north side and less in south side, which matched the distributions of the lowest temperature, average temperature and temperature dipping scale during chilling period. Our results are useful for guiding the chilling defense for relevant industries in Guangdong Province.

[Temporal and spatial change of climate resources and meteorological disasters under climate change during winter crop growing season in Guangdong Province, China.] / 气候变暖背景下广东冬种生产季气候资源和气象灾害的时空变化.

Trend analysis method was applied to analyze the general variation characteristics of the climate resources and meteorological disasters of growing season of the winter planting in Guangdong before (1961-1996) and after climate warming (1997-2015). Percentile method was employed to determine thresholds for extreme cold and drought in major planting regions, and the characteristics of extreme disasters since climate warming were analyzed. The results showed that, by comparing 1997-2015 with 1961-1996, the heat value in winter growing season increased significantly. The belt with a higher heat value, where the average temperature was ≥15 ℃ and accumulated temperature was ≥2200 ℃·d, covered the main winter production regions as Shaoguan, Zhanjiang, Maoming, Huizhou, Meizhou and Guangzhou. Meanwhile, the precipitation witnessed a slight increase. The regions with precipitations of 250-350 mm included Zhanjiang, Maoming, Huizhou, Guangzhou and Meizhou. Chilling injury in the winter planting season in the regions decreased, the belt with an accumulated chilling of <2 ℃·d covered the major geographic parts of the involved regions as Zhanjiang, Maoming, Guangzhou and Huizhou; and the belt with an accumulated chilling of 8-16 ℃·d covered the major geographic parts of Shaoguan and Meizhou. Meanwhile, the drought days decreased, the belt with drought days ≥50 included the major geographic parts of Zhanjiang, Maoming, Huizhou, Guangzhou and the belt with drought days <50 included the major geographic parts of Shaoguan. The typical case of the extreme disasters showed that the extreme chilling injury and drought in the main producing regions should not be overlooked. Maoming, Huizhou and Meizhou were at higher risk of extreme chilling injury, followed by Shaoguan and Guangzhou. Zhanjiang and Maoming faced the highest risk of extreme drought, Huizhou and Guangzhou took the second place, Shaoguan and Meizhou went last. During 1997-2015, the heat of winter season increased significantly, the trend of chilling and drought decreased, however, the extreme disasters occurred frequently and the risks were higher in winter production areas. It was suggested that the winter planting should be closely integrated with climate resources and the occurrence law of meteorological disasters in growing season.

Hierarchically interconnected porous scaffolds for phase change materials with improved thermal conductivity and efficient solar-to-electric energy conversion.

An ice-templating self-assembly strategy and a vacuum impregnation method were used to fabricate polyethylene glycol (PEG)/hierarchical porous scaffold composite phase change materials (PCMs). Hierarchically interconnected porous scaffolds of boron nitride (BN), with the aid of a small amount of graphene oxide (GO), endow the composite PCMs with high thermal conductivity, excellent shape-stability and efficient solar-to-electric energy conversion. The formation of a three-dimensional (3D) thermally conductive pathway in the composites contributes to improving the thermal conductivity up to 2.36 W m-1 K-1 at a relatively low content of BN (ca. 23 wt%). This work provides a route for thermally conductive and shape-stabilized composite PCMs used as energy storage materials.