Electricity Harvesting from Water Evaporation on Hierarchical Pore Gradient Silica Aerogel-Based Generators.

In this study, the electric energy harvesting capability of the hierarchical pore gradient silica aerogel (HPSA) is demonstrated due to its unique porous structure and inherent hydroxyl groups on the surface. Taking advantage of the positively charged surface of unwashed HPSA credited by the preparation strategy, poly(4-styrene sulfonic acid) (PSS) can be spontaneously adsorbed onto unwashed HPSA and shows gradient distribution due to the pore-gradient structure of HPSA. By virtue of the gradient distribution and the stronger ionization of PSS, PSS-modified HPSA (PSS-HPSA) shows enhanced electricity generation performance from natural water evaporation with an average output voltage of 0.77 V on an individual device. The water evaporation-induced electricity property of PSS-HPSA can be maintained in the presence of a low concentration of salt. The desirable salt resistance capability benefits from the unique 3D hierarchical porous structure of HPSA which ensures rapid water replenishment so as to effectively avoid the salt accumulation. The HPSA-based devices with the advantages of unique porous structure, easy functionalization, good physicochemical stability, good salt resistance capability, and eco-friendliness show great potential as water evaporation-induced electricity generators.

Dual S-scheme MoS2/ZnIn2S4/Graphene quantum dots ternary heterojunctions for highly efficient photocatalytic hydrogen evolution.

The layered chalcogenide ZnIn2S4 (ZIS) exhibits photo-stability and a tunable band gap but is limited in photocatalytic applications, such as hydrogen (H2) production, due to rapid carrier recombination and slow charge separation. To overcome these limitations, we have synthesized a ternary MoS2/ZIS/graphene quantum dots (GQDs) heterojunction, wherein MoS2 and GQDs are strategically attached to ZIS interlaced nanoflakes, enhancing light absorption across the 500-1500 nm range. This heterojunction benefits from dual S-scheme interfaces between MoS2-ZIS and ZIS-GQDs, establishing directed internal electric fields (IEFs). These IEFs accelerate the transfer of photoinduced electrons from the conduction bands of MoS2 and GQDs to the valence band of ZIS, promoting rapid recombination with holes and facilitating efficient catalytic reactions with plentiful photoinduced electrons stemmed from the conduction band of ZIS. As a result, the photocatalytic H2 production rate of the MoS2/ZIS/GQDs heterojunction is measured at 21.63 mmol h-1 g-1, marking an increase of 36.7 times over pure ZIS. This research provides valuable insights into designing novel heterojunctions for improved charge separation and transfer for solar energy conversion applications.

Polyelectrolyte Hydrogel-Functionalized Photothermal Sponge Enables Simultaneously Continuous Solar Desalination and Electricity Generation Without Salt Accumulation.

Technologies that can simultaneously generate electricity and desalinate seawater are highly attractive and required to meet the increasing global demand for power and clean water. Here, a bifunctional solar evaporator that features continuous electric generation in seawater without salt accumulation is developed by rational design of polyelectrolyte hydrogel-functionalized photothermal sponge. This evaporator not only exhibits an unprecedentedly high water evaporation rate of 3.53 kg m-2 h-1along with 98.6% solar energy conversion efficiency but can also uninterruptedly deliver a voltage output of 0.972 V and a current density of 172.38 µA cm-2 in high-concentration brine over a prolonged period under one sun irradiation. Many common electronic devices can be driven by simply connecting evaporator units in series or in parallel without any other auxiliaries. Different from the previously proposed power generation mechanism, this study reveals that the water-enabled proton concentration fields in intermediate water region can also induce an additional ion electric field in free water region containing solute, to further enhance electricity output. Given the low-cost materials, simple self-regeneration design, scalable fabrication processes, and stable performance, this work offers a promising strategy for addressing the shortages of clean water and sustainable electricity.

Confining Polymer Electrolyte in MOF for Safe and High-Performance All-Solid-State Sodium Metal Batteries.

Nanoconfined polymer molecules exhibit profound transformations in their properties and behaviors. Here, we present the synthesis of a polymer-in-MOF single ion conducting solid polymer electrolyte, where polymer segments are partially confined within nanopores ZIF-8 particles through Lewis acid-base interactions for solid-state sodium-metal batteries (SSMBs). The unique nanoconfinement effectively weakens Na ion coordination with the anions, facilitating the Na ion dissociation from salt. Simultaneously, the well-defined nanopores within ZIF-8 particles provide oriented and ordered migration channels for Na migration. As a result, this pioneering design allows the solid polymer electrolyte to achieve a Na ion transference number of 0.87, Na ion conductivity of 4.01×10-4 S cm-1, and an extended electrochemical voltage window up to 4.89 V vs. Na/Na+. The assembled SSMBs (with Na3V2(PO4)3 as the cathode) exhibit dendrite-free Na-metal deposition, promising rate capability, and stable cycling performance with 96 % capacity retention over 300 cycles. This innovative polymer-in-MOF design offers a compelling strategy for advancing high-performance and safe solid-state metal battery technologies.

Water State-Driven Catalytic Hydrolysis of Ammonia Borane on Cu3P-Carbon Dot-Cu Composite.

Hydrogen production from ammonia borane (AB) is usually governed by water activation, which is not only energy-intensive but also requires expensive and complicated catalysts. We here propose an integrated photocatalytic-photothermal system that dramatically improves water activation and lowers the transport resistance of H2 by means of intermediate state water evaporation. This system is constructed by covering nanocomposites (Cu3P-carbon dots-Cu) upon vertically aligned acetate fibers (VAAFs). As a result of superior hydration effect of VAAFs and local photothermal heating for rapid water evaporation, its hydrogen production efficiency from AB hydrolysis reaches over 10 times the particulate suspension system under solar irradiation. Mechanism analysis reveals that the rapid vaporization of intermediate water promotes the cleavages of O-H bonds in bound water and the adsorption reaction of AB and water molecules at active sites. Therefore, this work provides a novel approach to optimize catalytic reaction in thermodynamics and kinetics for the hydrolysis of AB.

Carbon dots-embedded amorphous nickel oxide for highly enhanced photocatalytic redox performance.

Amorphous materials reveal promising prospects in photocatalysis for the abundant active sites and tunable electronic configuration due to the lattice flexibility. However, the intrinsic lattice distortion could also cause the self-trapping effect and results in the recombination of photogenerated carriers. This disadvantage could be modified by the small size of amorphous domains for reducing charge migration distance. For this purpose, carbon dots (CDs) are introduced as the heterogeneous nucleus to regulate the configuration and composition of the amorphous nickel oxides for efficient utilization of photocarriers in catalytic reactions. The resultant nanocomposites a-NiOx/CDs show the densely distributed CDs embedded in the amorphous nickel oxide with dual valences of Ni2+ and Ni3+, and they reveal superior activities in photocatalytic oxidation and reduction compared with the single amorphous nickel oxide. The extraordinary photocatalytic performance is attributed to the synergetic function of their excellent separation efficiency of photoinduced charges and the cyclic conversion between Ni2+ and Ni3+ in the defects. This work provides inspiration for the modification and photocatalytic application of the amorphous materials.

Chemical treatment of biomasswastes as carbon dot carriers for solar-driven water purification.

A purely chemical method is demonstrated to treat a variety of biomass wastes for extracting cellulose nanofibrils (CNFs) with a consistent property. By hydrothermal reaction, carbon dots (CDs) can be easily grafted on the surface of CNFs to act as photo-thermal agents and enable fast water evaporation rate at 2.5 kg m-2h-1 with about 96.45% solar-to-vapor efficiency under one sun irradiation. This derives from good hydration ability of this system, which lowers the evaporation enthalpy. Moreover, this system not only adsorbs dye contaminants effectively by the formation of hydrogen bonds, but also possesses long-term antifouling solar desalination by means of rationally drilled millimeter-sized channels. Given the sustainable biomass resources and scalable fabrication process, this work offers a promising strategy towards construct low-cost evaporators with the excellent water purification performance.

A bifunctional nanozyme of carbon dots-mediated Co9S8 formation.

Controlling the size of nanocrystals and inhibiting their agglomeration are of paramount importance for achieving ideal catalytic performance. Here we discovered that carbon dots (CDs) are not only able to serve as reductants but also as stabilizers of ultrasmall Co9S8 nanocrystals by means of their surface terminal groups. As a result, ultrasmall Co9S8 nanocrystals are incorporated into porous carbon nanosheets formed by splicing CDs. The resultant nanocomposites display a rich pore structure accompanying with large specific surface area and outstanding bifunctional performances to mimic the catalytic activity of peroxidase and oxidase without exerting any external energy. More importantly, the unique architecture endows Co9S8 nanocrystals with high stability and good durability. The nanocomposites have been demonstrated as a colorimetric sensor for detection of ascorbic acid with a superior anti-interference ability as well as a detection limit of 0.2 µM. Our findings open new synthetic opportunities by tuning the interaction of CDs with the surrounding environment and enable advanced applications such as biomedicine and catalytic transformations.

Molybdenum Selenide/Porous Carbon Nanomaterial Heterostructures with Remarkably Enhanced Light-Boosting Peroxidase-like Activities.

Nanozymes have emerged as a fascinating nanomaterial with enzyme-like characteristics for addressing the limitations of natural enzymes. Nevertheless, how to improve the relatively low catalytic activity still remains challenging. Herein, a facile recrystallizing salt template-assisted chemical vapor deposition method was utilized to synthesize MoSe2/PCN heterostructures. This heterostructure displays remarkably enhanced light boosting peroxidase-like activities. Notably, the maximal reaction velocity of this heterostructure attains 17.81 and 86.89 µM min-1 [for o-phenylenediamine (OPD) and 3,3'5,5'-tetramethylbenzidine (TMB), respectively]. Moreover, various characterization means were performed to explore the mechanism deeply. It is worth mentioning that the photoinduced electrons generated by the heterostructure directly react with H2O2 to yield plentiful •OH for the effective oxidation of OPD and TMB. Therefore, this work offers a promising approach for improving peroxidase-like activity by light stimulation and actuating the development of enzyme-based applications.

Hydroxypropylmethyl Cellulose Modified with Carbon Dots Exhibits Light-Responsive and Reversible Optical Switching.

A light-responsive optical switching material is reported, which was obtained by incorporating carbon dots (CDs) into thermochromic hydroxypropylmethyl cellulose (HPMC). The ultrasmall size of CDs guarantees the considerable transparency of CDs/HPMC. Under illumination, CDs/HPMC shows rapid and reversible optical switching between transparent and opaque states due to the remarkable photothermal effect of CDs. Moreover, the interaction between CDs and HPMC enhances the light absorption and boosts the nonradiative recombination of photoexcited charge carriers that further promote the photothermal conversion of CDs, and also ensures the structural stability of the composite. The obtained CDs/HPMC with good reversibility and high sensitivity which can dynamically switch their transparency in response to weather conditions exhibits excellent solar modulation ability.

Boosting adsorption of heavy metal ions in wastewater through solar-driven interfacial evaporation of chemically-treated carbonized wood.

Once the adsorbent is selected, almost introducing larger specific surface area and more surface functional groups becomes the only way to improve its adsorption performance. However, this approach is generally limited in practical application for intricate and costly engineering steps. Herein, we provided a novel avenue for boosting adsorption activities towards specific metal ions in wastewater. Solar-driven interfacial water evaporation produces the localized temperature field and concentration gradient of metal ions inside small pores, endowing with a new sorption mechanism. By using chemically-treated carbonized wood as all-in-one solar absorption and metal ion adsorption system, we achieved higher water evaporation rate and heavy metal ion removal efficiency than carbonization-only wood reported previously. In particular, this system exhibited a strong dependence of specific metal ion adsorption capacity on solar intensity. Pb2+ adsorption capacity was enhanced by over 225% with the solar intensity increased to 3.0 kW·m-2. This could originate from the formed temperature field localized specially on the surface of adsorbents that not only induces Pb2+ concentration gradient near to solid-liquid interface but also activate inactive adsorption sites. Besides, the chemical-treated & carbonized wood showed excellent cyclic stability and can be directly utilized for wastewater treatment, recovery and reuse.

Facile Synthesis of Carbon Dots@2D MoS2 Heterostructure with Enhanced Photocatalytic Properties.

To better utilize carbon dots (CDs) as efficient photocatalysts, an excellent strategy of constructing CDs@MoS2 heterostructure is presented. Here a facile sonication-hydrothermal method is utilized to synthesize CDs@MoS2. Such heterostructure regulates the energy level configuration, and visible light absorption and the separation and transfer of photogenerated charges are enhanced remarkably, which is propitious for the production of more photoinduced charges and improvement of the heterogeneous photocatalytic activity. Meanwhile, the photocatalytic performance of CDs@MoS2 was obviously improved in methylene blue degradation. On the basis of a series of contrast experiments, the possible mechanism of the photocatalytic reaction is proposed. Therefore, this work offers a facile route for the design of a zero-dimensional/two-dimensional heterojunction for the adjustment of the energy level structure and the improvement in photocatalytic performance.

Nitrogen-doped carbon dots encapsulated in the mesoporous channels of SBA-15 with solid-state fluorescence and excellent stability.

A simple and low-cost approach is developed, by which nitrogen-doped carbon dots (NCDs) with a negative potential are assembled inside the mesoporous channels of SBA-15 via capillary force. The unique confined microenvironment leads to a strong interaction between confined NCDs and the inner surface of SBA-15, thus effectively avoiding the aggregation of NCDs. The resultant composite (NCDs-in-SBA-15) exhibits blue fluorescence similar to the NCD aqueous solution, and shows excellent structural, thermal and photostability. Solid NCDs-in-SBA-15 still emits fluorescence even after heat treatment at 400 °C under ambient atmosphere. In addition, NCDs-in-SBA-15 possesses remarkable resistance to acid/alkali solvents. Furthermore, NCDs-in-SBA-15 shows superior selectivity and adsorption capacity to Fe3+. The facile approach and these advantageous performances could make CDs meet the requirements of fluorescent materials in the solid state and then have wider applications.

Rapid cancer diagnosis by highly fluorescent carbon nanodots-based imaging.

Carbon dots (Cdots) with bright green fluorescence were applied to the rapid and selective cell imaging for a variety of cell lines. Different labeling distributions of hepatoma cells (HepG2) and normal human liver cells (LO2) were achieved using Cdots as imaging agents. For HepG2 cells, the Cdots could rapidly permeate the cell membrane and diffuse into the cytoplasm and nucleus within 3 min, and retained their location in the targets for 24 h. However, the Cdots exhibited bright fluorescence only in the cytoplasm of LO2 cell lines. Moreover, the Cdots were almost non-cytotoxic and exhibited superior photostability over a wide range of pH. Therefore, these Cdots have great potential for rapid, luminous and selective bioimaging applications, and are expected to be used as a nucleus-staining agent in cancer diagnosis. Graphical abstract ᅟ.

Carbon-Dot-Based Heterojunction for Engineering Band-Edge Position and Photocatalytic Performance.

A photocatalytic reaction is always governed by energy band configuration of the catalyst, but its modulation is challenging. Here, the adjustment of band-edge positions of Ag3 PO4 through fluorescent carbon dots is reported for the first time. Both Ag3 PO4 and carbon dots which keep the similar sizes constitute a heterojunction. Such heterostructure not only promotes visible light absorption, photogenerated charge separation, and transfer, but it also transforms photocatalytic activity of Ag3 PO4 from photooxidation to photoreduction due to the huge changes of band-edge positions. In addition, the heterojunction structure of carbon dots and Ag3 PO4 exhibits unique temperature-responsive photocatalytic activities and higher photocatalytic stability than the pure Ag3 PO4 . According to the contrast experiments and related characterizations, the possible mechanism of photocatalytic reaction is proposed. Therefore, this work offers an alternative route for adjusting energy band positions or tuning photocatalytic performance as well as for preparing novel carbon-dot-based heterostructure.

A simple, scalable approach for combining carbon dots with hexagonal nanoplates of nickel-based compounds for efficient photocatalytic reduction.

Hybrid nanostructures comprising disparate materials and having intricate shapes and facets are highly desired in photocatalytic applications requiring high selectivity. However, to produce such structures requires precise morphological control, and this is largely dictated by the stringent requirements of the reaction conditions, in addition to intricate, expensive, or tedious preparation steps. We present a simple, inexpensive, and scalable method for the preparation of hybrid nanostructures that combines carbon dots with hexagonal nanoplates of nickel-based compounds. The resultant heterostructure not only improves visible light absorption, but also exhibits enhanced photocatalytic activity for the reduction of 4-nitrophenol to 4-aminophenol when compared to carbon dots or hexagonal nanoplates of nickel-based compounds alone. The enhanced photocatalytic activity is due to the higher separation and transfer efficiency of photoexcited charge carriers at the interface between the carbon dot and hexagonal nanoplate of nickel-based compounds. This work opens up a straightforward and effective route to yield inexpensive and efficient photocatalysts for improved solar energy capture and conversion.

Cross-Linked Nanohybrid Polymer Electrolytes With POSS Cross-Linker for Solid-State Lithium Ion Batteries.

A new class of freestanding cross-linked hybrid polymer electrolytes (HPEs) with POSS as the cross-linker was prepared by a one-step free radical polymerization reaction. Octavinyl octasilsesquioxane (OV-POSS) with eight functional corner groups was used to provide cross-linking sites for the connection of polymer segments and the required mechanical strength to separate the cathode and anode. The unique cross-linked structure offers additional free volume for the motion of EO chains and provides fast and continuously interconnected ion-conducting channels along the nanoparticles/polymer matrix interface. The HPE exhibits the highest ionic conductivity of 1.39 × 10-3 S cm-1, as well as excellent interfacial compatibility with the Li electrode at 80°C. In particular, LiFePO4/Li cells based on the HPE deliver good rate capability and long-term cycling performance with an initial discharge capacity of 152.1 mAh g-1 and a capacity retention ratio of 88% after 150 cycles with a current density of 0.5 C at 80°C, demonstrating great potential application in high-performance LIBs at elevated temperatures.

Loading sulfur and nitrogen co-doped carbon dots onto g-C3N4 nanosheets for an efficient photocatalytic reduction of 4-nitrophenol.

A favorable interface for hybrid photocatalysts makes an important contribution in enhancing photocatalytic reactions. Herein we located sulfur and nitrogen co-doped carbon dots (SN-CDs) onto g-C3N4 nanosheets and achieved a novel SN-CD/g-C3N4 composite with a high visible-light photocatalytic reduction of 4-nitrophenol (4-NP). Compared to g-C3N4 nanosheets, the SN-CD/g-C3N4 composite possessed a wider light absorption. More importantly, the interaction of surface groups led to a favorable interfacial bonding between SN-CDs and g-C3N4 nanosheets, which facilitated the transfer of photoexcited electrons and holes, giving rise to an improved electron transport ability of the composite. In addition, the upward shift of the energy band of g-C3N4 nanosheets due to the location of SN-CDs led to a stronger reducibility of charge carriers. As a consequence, the photocatalytic performance of SN-CD/g-C3N4 has been remarkably improved in the photocatalytic reduction of 4-nitrophenol.

Multicolour Emission States from Charge Transfer between Carbon Dots and Surface Molecules.

The emissive states of carbon dots have been tuned by controlling the charge transfer process. The carbon dots couple with molecules, which are made of a benzene ring and different heteroatom substituents, through amino-carboxylic bonds that are generally identified as charge transfer promoters at the interface. New ways of radiative recombination are created due to the transfer of photo-excited electrons from carbon dots to the lowest unoccupied molecular orbital (LUMO) of the grafted molecules. By variation of the molecular orbital energy levels via heteroatom substituents in the benzene ring, the different optical properties and emission colors of the carbon dots were presented. This work opens up new opportunities for the application of carbon dots since different heteroatom substituents could lead to many possibilities for conjugation with drugs and biomolecules.

A solid reaction towards in situ hybridization of carbon dots and conjugated polymers for enhanced light absorption and conversion.

We for the first time developed a green and very simple method towards carbon-dot-incorporated poly(diphenylbutadiyne) nanohybrids (PDPB) through a solid reaction without the need of a template, a solvent and a surfactant. The incorporation of carbon dots into the PDPB nanostructures not only significantly improved visible light absorption but also enhanced photocatalytic performances.