Thermal Drying Process Research Articles

Determination of optimal air supply form on sludge convective drying process: A CFD-DEM study

Convective thermal drying is usually used in sludge dryers, and the air supply forms significantly affect the sludge drying efficiency. In this work, the drying process of multi-layered sludge is numerically simulated using a coupled computational fluid dynamics-discrete element method (CFD-DEM) approach. Better than our previous work, the current CFD-DEM model further considers the dynamic process of humidity within the flow field. Firstly, the CFD-DEM model is validated based on the mechanistic experimental data. Then, extensive numerical simulations are carried out to investigate the two-layered sludge drying process in the dryer, and the effects of two conventional air supply forms (Top-to-Bottom and Bottom-to-Top) as well as a novel air supply form (Side-assist) on the two-phase flow system are discussed. The simulation results provide in detail the dynamic processes of momentum, heat and mass (moisture) in the convective drying system under different working conditions. Following recommendations are presented to facilitate the operation of the dryer: Bottom-to-Top is better for sludge drying and tends to utilize less heat from the heat source compared to the Top-to-Bottom. The drying efficiency can be further improved by supplying the Side-assist with an optimal flow ratio of side-wind to bottom-wind. Numerical results show that the optimal flow ratio is related to the total air volume, the deflection angle and the side-wind temperature. The present study reveals in depth the impact mechanism of the air supply form on the convective thermal drying process of sludge, which contributes to the design and optimization of high-efficiency dryers.

Novel insights into the biopolymers transformation under wastewater sludge drying process at different temperatures in relation to drying behavior

The biopolymers are regarded as the leading role on the water evaporation in thermal drying process for sludges. Herein, the relationships between molecular transformation and water-holding capacities of biopolymers in sludge drying was investigated by multispectral methods coupled with FT-ICR MS technique. Our results showed that the exposure of hydrophobic groups in biopolymers was affected by drying temperature, causing significant differences upon water molecules binding and evaporation. In particular, below 120 °C, there was no obvious changes on the structural compositions of hydrophilia and hydrophobic compounds in sludge. Between 120 °C and 150 °C, the macromolecules were broken into smaller molecules with abundant hydrophobic groups exposing, resulted in efficient water evaporation with lower moisture in sludge. However, organics containing –NH and –C=O groups were aggregated via Maillard reaction at higher temperature (＞150 oC), the water molecules were trapped inside the Maillard products, and more energy was required to destroy the structure of organics for water evaporation, ended with higher moisture of dried sludges. In addition, a strong correlation between the hydrophilic index and CHON/CHONS distributions of extracted proteins in dried-sludge (DS) indicated that the water holding capacity and evaporation relied more on the spatial exposure of hydrophilic groups rather than their content. These implied that preventing the aggregation of hydrophilic functional groups (–NH and –C=O) in proteins was the key to eliminating the inhibitory of hydrophilic compounds in the biopolymers-bound water evaporation, and drying temperature below 150 °C was recommended. This study provides a mechanistic basis for better understanding of the biopolymer transformation (especially hydrophilic compounds) in drying process, and enable development of a more efficient and energy-saving drying procedure for sludges.

Unraveling the potential of non-thermal ultrasonic contact drying for enhanced functional and structural attributes of pea protein isolates: A comparative study with spray and freeze-drying methods

The challenge of preserving the quality of thermal-sensitive polymeric materials specifically proteins during a thermal drying process has been a subject of ongoing concern. To address this issue, we investigated the use of ultrasound contact drying (USD) under non-thermal conditions to produce functionalized pea protein powders. The study extensively examined functional and physicochemical properties of pea protein isolate (PPI) in powder forms obtained through three drying methods: USD (30 °C), spray drying (SD), and freeze drying (FD). Additionally, physical attributes such as powder flowability and color, along with morphological properties, were thoroughly studied. The results indicated that the innovative USD method produced powders of comparable quality to FD and significantly outperformed SD. Notably, the USD-PPI exhibited higher solubility across all pH levels compared to both FD-PPI and SD-PPI. Moreover, the USD-PPI samples demonstrated improved emulsifying and foaming properties, a higher percentage of random coil form (56.2 %), increased gel strength, and the highest bulk and tapped densities. Furthermore, the USD-PPI displayed a unique surface morphology with visible porosity and lumpiness. Overall, this study confirms the effectiveness of non-thermal ultrasound contact drying technology in producing superior functionalized plant protein powders, showing its potential in the fields of chemistry and sustainable materials processing.

A quantitative theory integrating solid surface hydrophilicity and pore structure features for non-phase-change drying of sewage sludge through gradient increase of ultrahigh filtration pressure

The sustainable application of thermal sludge drying process is limited by the high energy consumption due to the phase-change latent heat of moisture. This study proposed that the ultrahigh pressure filtration could realize the non-phase-change sludge drying. The lowest water content of 28.12 wt.% was realized by the filtration pressure of 21 MPa for the excess sludge with polyaluminium chloride as the conditioning agent. With the stepwise increase of filtration pressure employed (5-21 MPa), the diameter of solid pores was gradually narrowed to the same order of magnitude with the thickness of vicinal water film (i.e., 1-10 nm). As a result, the capillary water was transformed into the vicinal water, and the solid-water interface interaction played more crucial roles in water occurrence states. However, Hagen-Poiseuille equation was introduced to estimate the pore water outflow based on the pore wall hydrophilicity and the external filtration pressure, which implied that there can be always a sufficiently large driving force to maintain the water outflow rate no matter how the pore diameter is small and the sidewall is hydrophilic. Typically, the fitting results of excess sludge (R2=0.985, p-value<0.01) indicated that the pressure gradient of 2.11 × 109 Pa/m was required to maintain the pore water flow rate of 1.38 × 10−15 m3/s with the median pore diameter of 5.33 × 10−7 m. All these findings broke through the conventional cognition that only thermal drying process can decrease the sludge water content below 60 wt.%, and facilitated energy saving of sludge dewatering process through non-phase-change separation, i.e., ultrahigh pressure filtration.

Numerical Investigation on Thermal Drying Process of Sludges Based on CFD-DEM

Numerical Investigation on Thermal Drying Process of Sludges Based on CFD-DEM

Accumulation of Antioxidative Phenolics and Carotenoids Using Thermal Processing in Different Stages of Momordica charantia Fruit.

The bitter taste of M. charantia fruit limits its consumption, although the health benefits are well known. The thermal drying process is considered as an alternative method to reduce the bitterness. However, processing studies have rarely investigated physiochemical changes in fruit stages. The antioxidant activities and physiochemical properties of various fruit stages were investigated using different thermal treatments. The color of the thermally treated fruit varied depending on the temperature. When heat-treated for 3 days, the samples from the 30 °C and 90 °C treatments turned brown, while the color of the 60 °C sample did not change significantly. The antioxidant activities were increased in the thermally processed samples in a temperature-dependent manner, with an increase in phenolic compounds. In the 90 °C samples, the 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity presented a 6.8-fold higher level than that of nonthermal treatment in mature yellow fruit (S3), whereas the activity showed about a 3.1-fold higher level in immature green (S1) and mature green (S2) fruits. Regardless of the stages, the carotenoid content tended to decrease with increasing temperature. In terms of antioxidant activities, these results suggested that mature yellow fruit is better for consumption using thermal processing.

Facile synthesis of amino acids-derived Fe/N-codoped reduced graphene oxide for enhanced ORR electrocatalyst

A simple and green method for preparing Fe/N-codoped reduced graphene oxide nanosheets with high ORR and Zinc-air battery performance is presented. • 3D porous Fe/N-codoped reduced graphene oxide materials are prepared via a simple thermal drying and pyrolysis process. • Aspartic acid is introduced as an environment-friendly nitrogen and carbon source. • Iron nitrate serves as the pore forming agent and gas producer that prevent the agglomeration of graphene. • The optimized Fe-N-C/NG-3 material exhibits excellent ORR activity and applied to Zn-air battery. Here, a simple and green synthesis process of Fe/N-codoped reduced graphene oxide (Fe-N-C/NG) with high electrocatalytic activity for oxygen reduction reaction (ORR) is reported. The synthesis of 3D porous structure of Fe-N-C/NG composites involves thermal drying the mixture of graphene oxide (GO), iron nitrate and aspartic acid (Asp) directly, follow by pyrolysis the mixture. The Asp is introduced as an environment-friendly nitrogen and carbon source, and the iron nitrate serves as the pore-forming agent and a gas producer that prevents the agglomeration of graphene. The as-prepared Fe-N-C/NG exhibits 3D loose porous structure with larger specific surface area (245 m 2 g - 1 ). The Fe-NC/NG composite exhibits the onset potential of 0.91 V, a half-wave potential (E 1/2 = 0.83 V), low Tafel slope and four-electron selectivity (n = 3.99) in alkaline solution. Furthermore, the stability test manifests the outstanding stability of Fe-NC/NG electrocatalyst and a superior methanol tolerance than Pt/C electrodes. Particularly, when the prepared Fe-NC/NG-3 catalyst is used as an air electrode catalyst in an assembled Zn-air battery, it exhibits a high specific capacity of 848.2 mAh g Zn -1 and displays more stability than Pt/C. This work provides an effective strategy for preparing high ORR and Zn-air battery performance Fe/N-codoped reduced graphene oxide materials.

Design of silane-based UV-absorbing thin coatings on polyethylene films

UV-absorbing surfaces have received much attention and focus due to their relevance in a variety of research applications and industrial fields. However, these surfaces currently suffer from drawbacks such as instability due to leakage of the entrapped UV-absorbing compounds, complicated non-green synthetic processes, and/or lack of good optical properties. We propose a modified Stöber method where UV absorbing silane monomers containing the group2-hydroxy-4-(3-triethoxysilylpropoxy) diphenylketone (SiUV) in presence of the mesoporous producing surfactant cetyltrimethyl ammonium chloride (CTAC) was polymerized in an ethanol/water continuous phase under basic conditions. UV absorbing thin coatings onto polyethylene (PE) films were then spread with the former dispersion on corona-treated PE, followed by a thermal drying process. These films were highly UV absorbent and durable with excellent optical properties. Multiple applications of the UV absorbing coating were also tested and found to increase UV absorbance to approximately 100%, but on the other hand the optical properties were negatively affected. The coated samples underwent thermal shrinkage by 30% to simulate industrial applications. No significant change in UV absorbance and optical properties were discerned after their shrinkage. These results and synthetic simplicity indicate to the potential of the SiUV coated polymeric films to be used for industrial applications.

Enhancement of convective drying of a moist porous material with impinging slot jet by implementation of micro-encapsulated phase change material: A numerical feasibility study

The concept of convective drying of a moist porous material in the presence of micro-encapsulated phase change material is introduced in this study and then its favorable impact on drying efficiency is numerically investigated. In this regard, encapsulated PCM particles are dispersed inside the void part of porous medium while the moist sample is exposed to a compressible impinging slot jet. The transient evaporation process from a moist porous material exposed to a compressible air jet while PCM particles dispersing in water content of a porous sample is mathematically modeled and solved afterwards employing Finite Element Methods. A mathematical optimization technique is performed on the melting temperature of PCM to select a PCM appropriate to the thermal drying process. The numerical experiment in this work indicates that PCM facilitates the moisture removal process and dramatically reduces the water content in a typical convective drying. Investigating the transport mechanism, results show that PCM acts as a heat sink at the early stages of drying and then alternates to a heat source, releasing previously stored energy and internally heating the moist sample. According to the results, a 70.2% improvement in heat transfer enhancement is reported corresponding to 50% PCM volume fraction. The effects of PCM volume fraction, exit Reynolds number, and jet outlet temperature on PCM-equipped convective drying is considered.

Influence of phosphorus diffusion on the SiO2/4H-SiC (0001) interface during poly gate formation process

The work confirms the flat-band voltage (VFB) and SiC/SiO2 interface state density (Dit) characteristics 4H-of the SiC MOS capacitors, the oxide was obtained by performing a conventional thermal dry oxidation process on a 4H-SiC Si-face (0001) epi-wafer followed by Ar post-oxidation-annealing (POA). Poly gate and Al gate capacitors are formed on the same wafer and phosphorus is implanted into polysilicon to form the poly gate electrode. We found that the positive VFB shift is remarkable in the Al gate sample, the △VFB is about 1.4 V, but the shift is well suppressed in the Poly gate sample(△VFB ≈ −0.05 V), which suggests that the poly gate process reduce the instability of VFB. To some extent P diffusion from the Poly gate process plays an important role in compensating the charge trapping sites. The Dit of the Poly gate sample is also shown to be lower than the Al gate sample, particularly in the area of Ec-E > 0.4 eV. In addition, we confirmed that the Dit has a temperature dependence and thus is electrically active at elevated temperatures. Finally, secondary ion mass spectrometry (SIMS) measurements were carried out to investigate the differences between the Poly gate and Al gate samples. The results imply that there is a correlation between the increase in the phosphorus density at the interface and the observed reduction in Dit.

Study of Parameters Affecting Thermal Drying Process. (Dept. M)

Parameters affecting drying process has been studied experimentally as it associated with heat and mass transfer between porous bed to be dried and air which flows through the porous bed. To perform this study, a test rig is designed and constructed as it consists of vertical circular duct packed with wet porous bed which is made from clay balls of 20 mm in diameter. Drying process occurs as a result of forcing hot air vertically to pass through the wet porous bed, evaporation of moisture is existed in the bed due to the simultaneous heat and mass transfer. The studied operating parameters are inlet air temperature, inlet air mass flux, porous bed depth and porosity of balls. The average heat and mass transfer coefficients are estimated for flow of hot air through the wet porous bed. The results indicated that, the drying rate is directly proportional to inlet air temperature, mass flux of air, dimensionless bed depth and ball porosity. So, Drying process can be achieved in lower time as increasing both air mass flux and or inlet air temperature and decreasing bed depth. Also, heat transfer coefficient and mass transfer coefficient increase with increasing inlet air temperature, inlet air mass flux, and ball porosity, but they decrease with increasing bed depth. Comparison between the obtained experimental results and the previous work gave the same trend.

Characteristics of Moisture Transfer and Surface Crack Development of a Single Lignite Particle Driven by Humidity Difference.

The research on moisture transfer characteristics and surface crack development of a single lignite particle (SLP) driven by humidity difference is helpful to achieve a better understanding of the fragmentation characteristics of lignite during the moisture transfer process. This is of great significance to the safe operation of a drying system. The characteristics of moisture transfer within SLP driven by humidity difference were studied in different stages. Six drying equations commonly used in the literature were selected to describe the moisture transfer behavior. The apparent diffusion coefficient (Deff) of moisture in each stage was calculated to compare the driving forces of moisture transfer in different stages. The surface crack rate (CR) was used to quantitatively analyze the fragmentation characteristics of SLP caused by moisture transfer. The results showed that the moisture transfer process of SLP driven by humidity difference can be divided into three stages, and stage I is the main moisture removal stage. The larger the particle size, the longer the stage I, while less moisture is removed in this stage. A logarithmic drying equation best simulates the moisture transfer process of SLP. The larger the particle size, the larger the Deff value in each stage. The driving force of moisture transfer in stage I is the largest, which is the opposite of a thermal drying process. CR for SLP has experienced a rapid increase – stable at the highest value – rapid decrease – stable during the moisture transfer process driven by the humidity difference.

Comparison of Alum and Sulfuric Acid to Retain and Increase the Ammonium Content of Digestate Solids during Thermal Drying

Aluminum sulphate (alum, Al2(SO4)3·nH2O) has successfully been used to reduce ammonia loss from poultry litter, cattle feedlots and manure composting, but has not yet been utilized in the thermal drying process of digestate solids. The objectives of the present study were to evaluate the effects of alum addition on ammonium nitrogen (NH4+-N) content and phosphorus (P) solubility in dried digestate solids in comparison to the addition of concentrated sulfuric acid (H2SO4). Manure-based (MDS) and sewage sludge-based (SDS) digestate solids were chosen to conduct a drying experiment at four pH levels (original pH, 8.0, 7.5 and 6.5) and using two acidifying agents (alum, concentrated H2SO4). Alum addition increased the final NH4+-N content significantly from 1.4 mg g−1 in the non-acidified control up to 18 mg g−1 and 10.8 mg g−1 in dried MDS and SDS, respectively, which were higher levels than obtained with the addition of concentrated H2SO4. Moreover, alum considerably lowered the water extractable phosphorus (WEP) in raw and dried SDS by 37–83% and 48–72%, respectively, compared with the non-treated control. In contrast, concentrated H2SO4 notably increased WEP in raw and dried MDS by 18–103% and 29–225%, respectively. The comparison between the two acidifying agents indicated that alum had the potential to be an efficient and easy-handling alternative to concentrated sulfuric acid, resulting in higher NH4+-N content and lower P solubility.

Environmentally-friendly dewatering of sewage sludge: A novel strategy based on amphiphilic phase-transfer induced by recoverable organic solvent

This study proposed a novel strategy for sludge dewaterability improvement by eliminating the solid-liquid affinity through the polarity regulation of liquid phase. Initial screening experiments with different types of organic amendments (e.g., polar solvents, low-pole solvents, cytolytic reagents) found that acetonitrile and acetone could reduce specific resistance to filtration of sludge by 83.9% and 76.8%, respectively, at the solvent-sludge mass ratio of 1:1. The vacuum distillation and atmospheric distillation were both examined for the solvent recovery from filtered sludge cake and filtrate. Also, by considering the sensible heat for feedstock heating and enthalpy of solvent evaporation, the theoretical energy consumption of acetonitrile/acetone-enhanced sludge dewatering process was estimated to be at least 1/3 lower than that of the thermal drying process with the same treatment capacity, which indicated the energy saving potential of solvent-enhanced sludge dewatering process. Mechanism investigation was conducted by analyzing the surface functional groups of residual solid phase and the phase-transfer characteristics of amphiphilic compounds based on high-resolution Fourier transform-ion cyclotron resonance-mass spectrometry. It was found that the polarity of liquid phase dominated the phase-transfer of sludge compositions. The sufficient decrease in liquid polarity (dielectric constant < 55) would significantly eliminate the affinity of polar functional groups with the low-pole liquid phases, which induced the precipitation of amphiphilic proteins and substantially enhanced the solid-liquid separation. These findings suggest a promising technology for sludge dewaterability improvement by modifying the physical properties of liquid phase, which exhibits the obvious advantages in saving energy and material consumption.

A silsesquioxane-based flexible polyimide aerogel with high hydrophobicity and good adsorption for liquid pollutants in wastewater

A type of silsesquioxane-based flexible polyimide aerogel was synthesized by 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 4,4′-diaminodiphenyl and octa(aminopropylsilsesquioxane) (POSS-NH2) with a facile thermal curing and atmospheric drying process. POSS-NH2 was introduced into the polyimide backbone as a cross-linking agent. The obtained aerogel possessed high hydrophobicity with a water contact angle exceeding 143°. And the aerogels showed good cyclic adsorption capacity for various organic solvents, such as acetone, methanol, ethyl acetate, etc. After 15 adsorption experiments, the original adsorption capacity of the aerogels (more than 3 times their own weight) was still maintained. SEM and BET confirmed that the introduction of POSS-NH2 could form a larger pore structure inside the aerogel, thereby achieving an improvement in adsorption performance. The results indicated this kind of aerogel might be flexibly utilized as adsorbent materials for oil pollutants and harmful organic reagents in the field of wastewater treatment.

High Volumetric Energy Density of LiFePO4 Battery Based on Ultrasonic Vibration Combined with Thermal Drying Process

Increasing the compaction density of electrodes is an effective way to increase the volumetric energy density of the full battery. To avoid the problem of low compaction density, material breakage, and porosity decrease during the process of calendering, which greatly deteriorate the electrochemical performance of the battery, in this paper, for the first time, we use ultrasonic vibration-assisted densification technology combining with thermal drying technology to prepare the electrodes. Ultrasonic vibration reduces the friction among the powder particles during the drying process, so that the particles of active materials could aggregate more closely. And then, there are smaller displacements and sliding during the calendering process in ultrasonic vibration-assisted (UV–A) electrode than ordinary ones, which not only avoid the failure of the binder and the shedding of the carbon layer, also increase the number of connection points between material particles. The results show that the UV–A densification technology leads to improved volumetric energy density (increased by 5.3%, 6.6%, 7.6%, 11.6%, 13.4%, and 13.0% compared to the ordinary battery at 0.2C, 0.5C, 1C, 2C, 5C, and 10C, respectively), cycle performance and ion conductivity of full battery.

Nutritional and nutraceutical properties of raw and traditionally obtained flour from chestnut fruit grown in Tuscany

The study of local chestnut and traditional techniques related to their use and consumption are considered of primary importance to promote their nutritional/nutraceutical values. Fruit of four local chestnut cultivars (‘Carpinese’, ‘Pontecosi’, ‘Capannaccia’ and ‘Morona’) from Garfagnana (Italy) were analysed under nutritional and antioxidant aspects and compared with their flour obtained through a traditional thermal-drying process. Raw fruit contained significative amounts of P, K and Mg (~ 149, 1960 and 50 mg 100 g−1 dry weight, respectively) and they were characterised by a good moisture content (~ 49%) and starch (~ 50 g 100 g−1 dw). The traditional thermal-drying processes affected the carbohydrate content of dried chestnut showing a higher sucrose and lower starch content as compared to raw fruits. Traditional thermal-drying processes negatively influenced also total phenol content (TP) and total antioxidant activity: flours from all cultivars contained lower amounts of TP than raw fruit except for ‘Morona’ in which these compounds remained unchanged. This study provides new useful information about the evaluation of nutritional and nutraceutical characteristics of Tuscany local chestnuts and the effects of a traditional thermal-drying processing method, helping consumers and producers to valorise these “forest products”.

Volatilization characteristics of selenium during conventional and microwave drying of coal slime: an emerging contaminant in mining industry.

The priority feature of coal drying which accounts for its industrial use is moisture removal. Though much improvement is made in thermal-drying process, volatilization of harmful elements during coal slime drying is mostly ignored which has manifold environmental implications. In view of this, the present study attempted to investigate the moisture and selenium (Se) volatilization proportion during coal slime drying by using electric blast oven (conventional) and microwave oven (microwave) drying procedures. X-ray photoelectron spectroscopy (XPS) technique was employed to investigate the chemical changes of raw and dried coal. The results indicated that the microwave-drying process eliminates the moisture in line format, whereas, moisture content was removed slowly (initial stage) during conventional drying and then rapidly (final stage) with increasing drying period. It was confirmed that the microwave drying took less drying time to remove water and make the coal dried compared with the conventional drying. Volatilization proportion of Se to the atmosphere was 38.81 and 61.13% during conventional and microwave drying, respectively. Findings of XPS analysis demonstrated an increase in C-C and C-H content, while a decrease in C-O fraction on the coal surface, after execution of drying procedures. Microwave drying appeared not only energy efficient but also proved an optimized method for removing oxygen-functional groups than conventional drying methods. Peak fittings of XPS spectra gave indication of several oxidation forms including selenide, selenate, and oxide species in coal slime after drying. It was concluded that Se volatilization including speciation characteristics should be considered an indicator of efficiency for coal drying process from environmental safety perspective.

Investigation of Convective Heat and Mass Conditions in Squeeze Flow of a Hydro-magnetic Sutterby Fluid

Analysis regarding convective surface phenomenon has emerged to be effective approach to depict refinements in thermal features, since most of the heat/mass transfer surfaces are disclosed to a convective environment at specified parameters which cannot be achieved through energy analysis. The development in the dynamics of convective heat and mass transport is significant in understanding diverse engineering and industrial phenomena such as in thermal energy storage material drying process, transpiration cooling process, and many others. Keeping aforementioned usefulness in mind, the current analysis is aimed to demonstrate the convective features in squeezed Sutterby fluid flow through parallel surfaces. Magneto-hydrodynamic (MHD) theory is incorporated to describe the squeezing flow phenomenon. The Sutterby fluid model is accounted in order to specify the flow nature in squeezed channel. The top plate is assumed to be squeezed whereas the lower plate is at rest. The convective heating is incorporated at both lower and upper plates. Inspection of mass transfer has been accomplished in the occupancy of solutal convective conditions at the both surfaces. The equations governing the flow, heat and mass transport are first derived under the assumptions of low magnetic Reynolds number and negligible viscous dissipation, and then made non-dimensional by defining the similarity variables. Series solutions representing the flow velocity, temperature and concentration distributions are computed for definite values of power law index by utilizing convergent approach. Results are graphed and physical elucidated is seen for involved flow parameters. Variations in co-efficient of skin friction, Nusselt and Sherwood numbers are reported graphically. Significant findings in this attempt is that higher lower plate thermal and solutal Biot numbers strengthen the both heat and mass fluxes, while larger upper plate thermal and solutal Biot numbers weaken the heat and mass fluxes.

The 2D RGO-NiS2 dual co-catalyst synergistic modified g-C3N4 aerogel towards enhanced photocatalytic hydrogen production

The two-dimension RGO (reduced graphene oxide)-NiS2 dual co-catalyst synergistic modified g-C3N4 nanosheets aerogel is synthesized via the continuous thermal oxidation etching-hydrothermal method-freeze drying process. The results of scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) imply that the RGO-NiS2 dual co-catalyst is introduced into the aerogel system successfully. The photocatalytic activity of the RGO-NiS2 synergistic modified g-C3N4 aerogel remarkably exhibits an enhancement of 67 times than that of simplicial g-C3N4. Further, the photocatalytic process and the mechanism of the photocatalytic hydrogen production enhancement are studied, which is ascribed to RGO-NiS2 dual co-catalyst synergistic modification, including the Pt-like behavior of the NiS2 and the high conductivity and large specific surface area of the RGO.