Hydrothermal Treatment Temperature Research Articles

Synthesis of novel green phosphate pigments with phosphophyllite composition

AbstractA new green pigment with the composition of phosphophyllite was synthesized using zinc oxide, iron oxalate, and phosphoric acid in a hydrothermal process. The effects of hydrothermal treatment temperature and time were investigated. In order to obtain pigments with a variety of colors, compounds with related compositions were also prepared. Further, samples were prepared with nitrogen bubbling to suppress the oxidation of iron. The composition of the fabricated samples was evaluated by X‐ray diffraction and infrared spectra. The color of the samples was evaluated by ultraviolet‐visible reflectance spectra and L*a*b* color space. The samples prepared in this study were a mixture of Zn2Fe(PO4)2•2H2O, the target compound, and iron oxalate, the raw material. The obtained samples were yellow to green in color. The condition that yielded the best green pigment was hydrothermal treatment at 180°C for 20 h with nitrogen bubbling.

Hydrothermal treatment: An efficient food waste disposal technology.

The quantities of food waste (FW) are increasing yearly. Proper disposal of FW is essential for reusing value-added products, environmental protection, and human health. Based on the typical characteristics of high moisture content and high organic content of FW, hydrothermal treatment (HTT), as a novel thermochemical treatment technology, plays unique effects in the disposal and utilization of FW. The HTT of FW has attracted more and more attention in recent years, however, there are few conclusive reviews about the progress of the HTT of FW. HTT is an excellent approach to converting energy-rich materials into energy-dense fuels and valuable chemicals. This process can handle biomass with relatively high moisture content and allows efficient heat integration. This mini-review presents the current knowledge of recent advances in HTT of FW. The effects of HTT temperature and duration on organic nutritional compositions (including carbohydrates, starch, lipids, protein, cellulose, hemicellulose, lignin, etc.) and physicochemical properties (including pH, elemental composition, functional groups, fuel properties, etc.) and structural properties of FW are evaluated. The compositions of FW can degrade during HTT so that the physical and chemical properties of FW can be changed. The application and economic analyses of HTT in FW are summarized. Finally, the analyses of challenges and future perspectives on HTT of FW have shown that industrial reactors should be built effectively, and techno-economic analysis, overall energy balance, and life cycle assessment of the HTT process are necessary. The mini-review offers new approaches and perspectives for the efficient reuse of food waste.

Metal-doped carbon-supported/modified titanate nanotubes for perfluorooctane sulfonate degradation in water: Effects of preparation conditions, mechanisms, and parameter optimization

Metal-doped, activated carbon (AC) supported titanate nanotubes (Me/TNTs@AC) have been shown promising for photocatalytic degradation of per- and polyfluoroalkyl substances (PFAS). However, the preparation recipe of the adsorptive photocatalysts has not yet been optimized in terms of type and content of precursor ACs and the metal dopants as well as synthesizing conditions. In this work, the photocatalytic performance of Me/TNTs@AC was evaluated based on the effectiveness in defluorination of pre-sorbed perfluorooctane sulfonic acid (PFOS) after 4-h UV irradiation. Based on the experimental results, the highest photocatalytic mineralization efficiency (66.2 %) of PFOS was achieved using Ga/TNTs@AC prepared under the following conditions: Filtrosorb-400® = 50 wt%, Ga = 2 wt%, hydrothermal treatment temperature = 130 °C, hydrothermal duration = 72 h, and calcination temperature = 550 °C. To understand the underlying mechanisms, selected materials were characterized via X-ray diffraction, the BET surface area and pore volume, UV–vis diffuse reflectance spectrometry, and photoluminescence. The results revealed that the superior photoactivity of Ga/TNTs@AC is attributed to the Ga-facilitated formation of pure crystallized anatase phase during the calcination, high UV light absorption, formation of microscale hybrid AC-anatase-Ga phases, and oxygen defects induced by Ga3+. The information can facilitate preparation and optimization of composite photocatalysts for efficient adsorption and photocatalytic degradation of PFAS in water.

Effects of lignocellulosic biomass type on nutrient recovery and heavy metal removal from digested sludge by hydrothermal treatment.

Sludge is a nutrient-rich organic waste generated from wastewater treatment plants. However, the application of sludge as a nutrient source is limited by its high contents of water and pollutants. In this study, the effects of biomass type on nutrient recovery and heavy metal removal from digested sludge by hydrothermal treatment (HTT) were investigated. Blending biomass with digested sludge for HTT at 180-240°C increased the recovery of nitrogen in the treated solids. At the HTT temperature of 240°C, HTT with hardwood sawdust led to the highest nitrogen recovery of 70.6%, compared to the lowest nitrogen recovery of 36.5% without biomass. Blending biomass slightly decreased the recovery of phosphorus compared to those without biomass. Nevertheless, the lowest phosphorus recovery of 91.3% with the use of hardwood sawdust at the HTT temperature of 240°C was only ∼7.0% less than that without biomass. Blending biomass reduced the contents of macro-metals such as Ca, Fe, Mg and Al in treated solids but the metal contents varied with different biomasses. Regarding the heavy metals, the use of rice husk did not decrease the contents of Ni and Co while blending bagasse did not decrease the content of Cr at HTT temperatures of 210°C and 240°C compared to the use of other biomasses. The different effects of biomass type on nutrient recovery and heavy metals were likely related to the types and abundances of organic acids such as acetic acid, oxygen-containing functional groups such as C-OH and COOH, oxide minerals such as silica from biomasses and the overall effects of these factors. This study provides very useful information in selection of lignocellulosic biomass for HTT of sludge for nutrient recovery and heavy metal removal.

Hydrochar prepared from municipal sewage sludge as renewable fuels: Evaluation of its devolatilization performance, reaction mechanism, and thermodynamic property

Hydrothermal treatment (HT) of sewage sludge (SS) is a promising method to improve its dewaterability. Effect of HT on devolatilization performance, kinetic parameters, and thermodynamic property during the pyrolysis of SS was investigated by thermogravimetric analysis (TGA), isoconversional method, and master plots method. Derivative thermogravimetry (DTG) curves showed two distinct devolatilization peaks #1 at 283.21 °C and #2 at 327. 43 °C along with a shoulder between 400 and 600 °C. HT temperature influenced peak #2 more significantly as its peak devolatilization rate decreased consecutively from 4.25 % to 1.70 %∙min−1. Meanwhile it moved towards higher temperature and overlapped with the shoulder ultimately. The value of comprehensive pyrolysis index (CPI) decreased greatly from 3.37 × 10−5 to 1.24 × 10−6 %3∙°C−3∙min−2 with HT temperature. Activation energy was determined by Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Starink, and Friedman methods. It generally increased against conversion with diverse variation patterns. Its average value reduced obviously after HT. Despite HT, all samples followed identical Avrami-Erofeev model with decreased order of reaction from 7.60 to 6.56. The variation trends of enthalpy, Gibbs free energy, and entropy verified that HT improved the thermal stability of SS, which coincided with CPI. Pyrolysis process of SS evolved from ordered state to disordered state, indicating increased reactivity due to the probable catalytic effect of inorganics in the ash. The work provides guidance for the design, optimization, and upscale of pyrolysis reactors and operation parameters when SS is utilized as renewable fuels.

Facile temperature-controlled preparation of nanowire OMS-2 and its high performance in peroxymonosulfate-activated catalytic degradation of organic pollutants

Currently, nanowires present a type of unique one-dimensional materials showing promising prospects in many fields. The octahedron molecular sieve (OMS-2, with chemical compositions of K[Formula: see text][Formula: see text]Mn8O16) materials are utilized extensively as efficient catalysts for numerous critical reactions. In this work, it was found that the evolution from [Formula: see text]-MnOOH microrod to OMS-2 nanowire can be induced facilely by altering the temperature of hydrothermal treatment. The obtained OMS-2 nanowire exhibited high catalytic activity and high durability in peroxymonosulfate (PMS) activated degradation of rhodamine B (RhB) or methylene blue (MB). Under optimum conditions (OMS-2 catalyst: 0.1 g⋅L[Formula: see text]; RhB or MB: 8 mg⋅L[Formula: see text], 100 mL), the degradation can be completed within 10 min. The possible reason for OMS-2 nanowire’s high performance was also proposed.

Characterization and nutritional value of hydrothermal liquid products from distillers grains

Hydrothermal liquid products (HLPs) produced by hydrothermal treatment (HTT) contain a large amount of nitrogen, phosphorus and other substances, while the environmental problems caused by arbitrary discharge. This work explored the effects of temperature, reaction time and solid-liquid ratio on the chemistry of HLPs of two different distillers grains, with a focus on nutrient composition. Increased HTT temperature was related to increased HLPs pH, dissolved organic carbon content, and aromaticity, and decreased electrical conductivity. Maximum nutrient extraction efficiencies observed for NH4+-N, NO3−-N and PO43− were 92.0, 89.9, and 94.3%, respectively. Response surface methodology showed that the release of nutrient extraction efficiency was the greatest at the hydrothermal treatment of 200 °C for 1 h, and using a solid/liquid ratio of 10%. Comparative studies, the nutritional value of HLPs are appropriate for use as an agricultural fertilizer, and its use as a substitute for synthetic fertilizers could increase the sustainability and profitability of farming.

Effect of High-Temperature Hydrothermal Treatment on Chemical, Mechanical, Physical, and Surface Properties of Moso Bamboo

Bamboo is an ideal material as it is green, fast-growing, and easy to process. However, the low dimensional stability may limit the application of bamboo due to its richness in hydrophilic groups. Thus, an effective and environment-friendly modification is needed to solve the aforementioned problems. This study employed high-temperature hydrothermal treatment for the modification of bamboo to offer technical support to further promote the application of bamboo materials. Bamboo was heated at various temperatures (120–160 °C) for diverse durations (60–120 min), and the chemical composition, mechanical properties, dimensional stability, and surface color were studied. Results revealed that the parenchyma cells of bamboo were deformed and the parenchymal cell lumen without starch granules after treatment at 160 °C for 120 min. The cellulose and hemicellulose content of bamboo decreased, and the lignin content increased in relative terms as the temperature and time of high-temperature hydrothermal treatment continued to rise. The mechanical properties of bamboo declined after high temperature hydrothermal treatment, and the modulus of rupture (MOR) and modulus of elasticity (MOE) of bamboo at 160 °C for 120 min decreased by 47.11% and 16.14%, respectively, compared to untreated bamboo. The swelling test indicated that the dimensional stability of the bamboo was improved, and the swelling ratio of the bamboo was reduced through the high-temperature hydrothermal treatment. The tangential and radial swelling coefficients of bamboo were reduced by 53.28% and 53.59%, respectively, after treatment at 160 °C for 120 min compared to untreated bamboo. The bamboo surface color was darkened after heat treatment, which gives the bamboo better surface decorative properties.

Assessment of hydrothermal parameters in the wet synthesis of α- and β-BiTaO4 by in situ synchrotron X-ray diffraction

Synchrotron X-ray diffraction was used for in situ monitoring of hydrothermal precursors calcination to obtain BiTaO4 in the orthorhombic (α) and triclinic (β) crystal phases. Different precursors were prepared varying time (24 and 48 h) and temperature (150 and 200 °C) of hydrothermal treatment. According to the results of in situ X-ray analysis during calcination of the precursors, the α- and β-BiTaO4 phases were achieved from the hydrothermal precursors treated at 200 °C. When the hydrothermal treatment time was carried out for 24 h, a precursor with Bi1−xTaxO1.5−x (fluorite structure, like δ-Bi2O3) and BiOCl phases was obtained, which evolved to Bi24Cl10O31 phase with heating. The presence of the chlorine-containing phases and the low crystallinity of the hydrothermal precursor contributed to the formation of β-BiTaO4. When the precursor is obtained with 48 h of hydrothermal treatment, only the Bi1−xTaxO1.5−x crystalline phase was identified and when heated it evolved to α-BiTaO4 phase at 550 °C. This is the first time that the pure orthorhombic phase is obtained from a wet synthesis method. All identified phases were confirmed by Rietveld refinement.

Decrease the effective temperature of hydrothermal treatment for sewage sludge deep dewatering: Mechanistic of tannic acid aided

The formation of refractory compounds and high nitrogen concentrations in filtrates is the bottleneck of hydrothermal treatment (HT) for sludge deep dewatering. To simultaneously solve these two problems, tannic acid (TA)-aided HT was firstly developed in this study. TA addition improved dewaterability under all investigated HT temperatures by improving the sludge relative hydrophobicity. Moreover, the effective HT temperature was reduced from 180 to 160 ℃. The soluble extracellular polymeric substances (S-EPSs) of the sludge hydrothermally treated at 160 ℃ under the optimal TA dose (0.15 mmol/g total solids) contained 47.27% less total organic nitrogen than the S-EPSs of the raw sludge. This result means that the corresponding filtrate contained lower concentrations of refractory compounds and nitrogen than those under the conventional HT conditions and thus could be more easily treated. Furthermore, the changes in the protein secondary structure and the interaction of TA with high-molecular-weight (HMW) proteins in S-EPSs were found to be highly relevant (p < 0.05) to the improvement of sludge dewaterability. With increasing HT temperature (120–180 ℃), the S-EPS HMW proteins with numerous hydrophilic functional groups (hydroxyl and carboxyl) were hydrolyzed, and their secondary structures unfolded; consequently, more sites were exposed for hydrophobic binding with TA, and the TA–protein interaction was more stable and spontaneous. The precipitation of protein with TA also increased with the HT temperature. Thus, TA-aided HT improves protein precipitation and sludge dewaterability through protein structure destruction and the production of more hydrophobic binding sites for TA. The identification of the influencing mechanisms on SS EPS–TA interaction mode and binding capacity are conducive to the further upgrading of TA-aided HT for engineering applications.

The three-stage effect of hydrothermal treatment on sludge physical-chemical properties: Evolution of polymeric substances and their interaction with physicochemical properties

Hydrothermal treatment (HT) is effective for the deep dewatering of sewage sludge (SS); however, the effective temperature generally exceeds 180 ℃, resulting in the production of refractory compounds in the sludge filtrates. To explore a new process based on HT, achieving ideal dehydration efficiency at lower temperatures, it is essential to identify the key sludge dewatering mechanism under different HT stages. In this study, the relationship between the properties of sludge polymeric substances (components and molecular structures) and the physical-chemical properties of sludge flocs during HT (120–260 ℃) was investigated. The results indicated that the SS surface hydrophilicity/hydrophobicity was mainly responsible for sludge dewaterability in the solubilization (120 ℃) and hydrolyzation stages (140–180 ℃), while the mechanically bound water and capillary force were the main limiting factors of sludge dewaterability during the carbonization stage (200–260 ℃). Moreover, in the solubilization stage (120 ℃), a plenty of high-Mw (Mw > 70 kDa) polymeric substances with numerous hydrophilic functional groups and a compact structure were released from the intracellular region to the outer layer, which improved the hydrophilicity of sludge floc surface and deteriorated the sludge dewaterability. With the hydrolysis of the polymeric substances (140–180 ℃, hydrolyzation stage), the destruction of proteins secondary structures and peptide chains exposed more hydrophobic groups, resulting in the release of bound water and improvement of sludge dewaterability. At HT temperatures of 200–260 ℃ (carbonization stage), dehydration and amine aldehyde condensation occurred, benefiting the formation of fixed carbon and smooth morphology structure of SS, reducing the capillary force–induced water-holding capacity of sludge flocs. The establishment of the three-stage influencing theory and the identification of key influencing factors are conducive to the further regulation and upgrading of HT.

Organic Template‐Free Synthesis of Mesoporous ZnO Microparticles by Sol‐Gel Method and Low‐Temperature Hydrothermal Treatment

Mesoporous zinc oxide microparticles were synthesized by the sol‐gel method, followed by hydrothermal treatment at three different temperatures (100°C, 120°C, and 140°C), confirming that the method is fast, simple, reproducible, and ecological. To carry out the synthesis of the samples, zinc acetate was used as a precursor and sodium hydroxide as a precipitating agent. From the results obtained, the sample that shows the highest mesoporosity was the one synthesized at a hydrothermal treatment temperature of 140°C, obtaining an average particle size of 5 μm and a pore diameter of 1.7 nm. The importance of the results obtained was that mesoporous xerogel microparticles were obtained without using any type of organic template.

Characteristic of the medical waste for solid fuel by the hydrothemral treatment

The changes in the property of general medical waste at different hydrothermal treatment temperatures and their potential application as fuel were examined to determine the utilization potential in the conventional incineration method via hydrothermal treatment. Among the different medical wastes studied, the fuel properties (e.g., calorific value) of cotton and gauze improved, while those of syringes and masks decreased, with increasing hydrothermal treatment temperature. For the hydrothermal treatment of medical waste, a temperature of approximately 230 °C was considered appropriate for fuel efficiency, while complying with legal standards. However, severe corrosion was observed in the hydrothermal treatment reactor for medical waste. The PVC found in medical waste was transformed to HCl during thermal decomposition; this HCl dissolved in water to lower the pH and cause strong corrosion inside the reactor. The results of the combustion test for medical waste performed with and without hydrothermal treatments showed that large volumes of the air pollutant CO were generated during ignition, which reduced as the combustion stabilized. For medical waste with hydrothermal treatment, the combustion time was extended owing to increased amount of fixed carbon and the decrease, and the CO concentration dropped to 60 ppm. No significant change was detected in NOx concentrations after the hydrothermal treatment.

Effect of hydrothermal treatment on deep dewatering of digested sludge: Further understanding the role of lignocellulosic biomass

In this study, lignocellulose-assisted hydrothermal treatment (HTT) of digestated sludge was studied to further understand the role of biomass in HTT and its effect on subsequent sludge dewatering. HTT of sludge-biomass mixtures at 180 °C for 60 min at a sludge/biomass total solids (TS) ratio of 1:1 led to solid residue moistures of 36%–40% after dewatering using a hydraulic press at 24 MPa, compared to 69.5% without biomass. Further investigation showed that organic acids, especially acetic acid generated from lignocellulosic biomass hydrolysed extracellular polymeric substances (EPS), especially EPS-protein, and improved sludge dewaterability. The role of organic acids was further verified with the addition of 10.0 g/L acetic acid for HTT of sludge at 180 °C in the absence of biomass. It was also observed that in HTT of sludge with 10.0 g/L acetic acid, protein nitrogen was converted to more stable forms of nitrogen such as pyrrole‑nitrogen and quaternary‑nitrogen. However, HTT with acetic acid alone resulted in dewatered solids with high ash contents, which may limit their applications as soil amendments. Combination of biomass and acetic acid with a sludge/biomass TS ratio of 3:1 and acetic acid loading of 10.0 g/L at a HTT temperature of 180 °C for 60 min led to solid moistures of 50.5% with hardwood sawdust and 57.7% with sugarcane bagasse after dewatering at 3 MPa, corresponding to total weight reductions of 66.3% and 55.7%, respectively. In contrast, HTT of sludge at 180 °C for 60 min without acetic acid and biomass resulted in a solid moisture of 76.6% after dewatering at 3 MPa and a corresponding weight reduction of 49.5%. With the use of biomass and acetic acid in HTT, the treated and dewatered solids also had increased carbon content and reduced ash content. These dewatered solids may be used as potential soil amendments though the properties related to soil applications need to be considered in future studies.

High-surface-area porous carbons produced by the mild KOH activation of a chitosan hydrochar and their CO2 capture

Hydrothermal treatment of biomass is effective in producing hydrochar, but the product usually has a low surface area and is not suitable for direct use as an adsorbent for CO2 capture. We report the use of chitosan as a precursor for carbon prepared by a combination of hydrothermal treatment and mild KOH activation. The effect of an additive salt (eutectic salt of KCl/LiCl with a mass ratio of 5.5/4.5) in the hydrothermal treatment and activation temperature on the porosities and surface chemical states of the obtained carbons and their CO2 capture were studied by N2 adsorption, XPS, SEM and XRD. Results indicated that the porosities of the carbons were increased by increasing the activation temperature. The salt additive introduced mesopores in the hydrochar and slightly reduced the surface area of the porous carbon after activation, but was useful in increasing the number of N-species during hydrothermal treatment and activation. The carbons produced using the salt additive had much larger CO2 uptakes under ambient conditions than those prepared without the salt, suggesting that porosity is not the only factor that determines the CO2 uptake. The CO2 uptake on the carbon activated by KOH at 600 °C produced from the salt-assisted hydrochar was the highest (as high as 4.41 mmol/g) although its surface area was only 1249 m2/g, indicating that CO2 uptake was determined by both the microporosity and the active N-species in the carbon.

Effect of water molecules at different temperatures on properties of cellulose based on molecular dynamics simulation

Six hybrid models of cellulose amorphous region and water molecules were established by using a molecular dynamics software to simulate changes of cellulose and water molecules during bamboo hydrothermal treatment. The results indicated that in the range of hydrothermal treatment temperature of bamboo from 150 to 240 °C, the diffusion coefficient of water molecules increased with the increase of temperature, conducive to the processing efficiency of hydrothermal treatment. The mean square displacement (MSD) of the bamboo cellulose chain increased with the increase of temperature, not conducive to the thermal stability of cellulose. The energy change of the system predicts that a higher hydrothermal treatment temperature will result in faster material aging degradation. The comprehensive analysis of mechanical parameters showed that when the hydrothermal treatment temperature did not exceed 180 °C, bamboo cellulose had better plasticity and toughness.

열수 처리 온도 및 시간에 따른 생강 슬라이스의 이화학적 특성 및 항산화능

This study was conducted to determine the optimal hydrothermal pretreatment conditions for manufacturing processed ginger products. Ginger slices heated at different temperatures (60-100°C for 1 h) for varying durations (1-5 h at 80°C) were compared in terms of their physiochemical properties, antioxidant activities, and functional compound contents. The pH and soluble solid content decreased with increasing hydrothermal treatment temperature. Browning occurred at temperatures &gt; 80°C. The 2,2-diphenyl-1-picrahydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging were highest after heating at 80°C for 1 h, and the total phenolic compound content showed a similar trend. As the hydrothermal treatment temperature and duration increased, the 6-gingerol content decreased and the 6-shogaol content generally increased. Based on sensory testing of ginger jeonggwa (with sugar syrup) prepared using hot water-treated ginger slices, the optimal hot water treatments were conducted at 70 and 80°C for 1 h, with no significant difference between these temperatures in terms of smell, taste, and texture. Therefore, hydrothermal treatment of ginger at 70-80°C for 1 h was a suitable to improve the functionality and antioxidant ability while maintaining the sensory quality. Therefore, this may be used in the production of processed ginger.

Critical analysis of zeolite 4A synthesis through one-pot fusion hydrothermal treatment approach for class F fly ash

In this study, ‘‘One-pot fusion assisted hydrothermal synthesis’’ approach was employed to understand the nucleation and crystallization behaviour of the fusion product of Class F fly ash for zeolite 4A synthesis. Two sets of experiments were conducted by tailoring the control parameter of H 2 O/Na 2 O molar ratio (L/S) to investigate the nucleation and crystallization behaviour of zeolite 4A. The molar ratios of SiO 2 /Al 2 O 3 and Na 2 O/SiO 2 were tuned before alkali fusion by adding different amounts of Al(OH) 3 to the fly ash along with the alkali agent, Na 2 CO 3 . Under the conditions of 12h aging at 47 °C and 7h crystallization at 90 °C, the sample with high L/S ratio (3.1 Na 2 O: 2.2 SiO 2 : 1.0 Al 2 O 3 : 79.2 H 2 O) yielded pure phase of Zeolite 4A with 94% relative crystallinity, while the sample with low L/S ratio (3.1 Na 2 O: 2.2 SiO 2 : 1.0 Al 2 O 3 : 42.2 H 2 O) resulted in the highest sodalite impurity. In general, the alkalinity level was observed to be the most dominant factor among all synthesis parameters. Nevertheless, low L/S ratio led to rapid crystallization in just 2.5h at 75 °C. Because of the dependency on the alkalinity level, the dissolution of low-carnegieite (LC) was determined as the decisive factor in the formation of zeolite 4A from the fusion product. The total time of hydrothermal treatment and aging temperature were the other main factors. The crystal growth of zeolite 4A was more sensitive to changes induced by crystallization time and temperature at high L/S ratio. Relative crystallinity of zeolite 4A varied in an expanded range in terms of crystallization time (36%–86%) and temperature (25%–73%) at high L/S ratio. • The control parameter L/S ratio led to sharp differences in crystallization behaviour. • Dissolution of low-carnegieite was decisive on the %crystallinity of zeolite 4A. • Alkalinity level strongly influenced dissolution of low carnegieite. • Alkalinity level was the major factor on the nucleation and crystallization. • Faster dissolution of low-carnegieite resulted in formation of sodalite.

Mechanism insights into hydrothermal dewatering of food waste digestate for products valorization

Poor dewaterability is a bottleneck of the disposal of digestate from food waste (DFW). However, the dewatering mechanism remains unclear due to the complex composition of DFW. Understanding the dewatering mechanism, as well as the transformation of organic/inorganic matters is essential for the DFW management and valorization. In this study, the distribution, transformation, and complex interplay of organic and inorganic matters at different Hydrothermal treatment (HTT) temperatures were comprehensively analyzed to explore the hydrothermal dewatering mechanism of DFW. When HTT was conducted in the temperature range of 120–180 °C, the interstitial water was released as surface or free water because of membrane breaking and size reduction of the solid substrate. Releasing divalent cations increased the Zeta potential of the bulk solution. The weaker electrostatic repulsion between suspended particles made them easier to settle as the centrifugation cake. When the temperature of HTT was above 180 °C, polymerization and aromatization reactions took place gradually for organic matters, and the bound water was further removed. The generated humic substances were more hydrophobic than the raw material. In addition, the humic substance could combine with cationic metals, which decreased the zeta potential of the bulk solution but promoted the aggregation of nanoparticles and enhance the dewaterability of DFW.

Hollow ZnO microspheres self-assembled from rod-like nanostructures: morphology-dependent linear and Kerr-type nonlinear optical properties

Hollow nanostructures have attracted attention because of their unique physiochemical properties and broad potential applications in electronics, optics and photonics. In this study, a facile hydrothermal approach was developed to fabricate hollow ZnO microspheres via self-assembled rod-like nanostructures. The morphology-controlled synthesis was conducted by altering hydrothermal treatment temperature (150, 200 and 250 °C) in solutions containing zinc acetate dihydrate precursor and glycerol as the stabilizing agent. The morphological observations indicated that hydrothermally grown ZnO architectures could be reasonably adjusted by modulating hydrothermal reaction temperature. Possible growth routes are proposed to elucidate the formation process of ZnO microspheres with the rod-like nanostructures. Morphology-dependent absorbance and emission along with red-shifts with improved crystalline qualities were observed with increasing hydrothermal growth temperature. Kerr-type nonlinear optical characteristics examined using single-beam Z-scan technique in the near infrared spectral range under nanosecond Nd-YVO4 laser pulses showed positive values of nonlinear refraction providing an evidence of self-focusing behaviors at the excitation wavelength of 1064 nm in all the samples studied. The highest Kerr-type nonlinear susceptibility was estimated to be 2.31 × 10–6 esu for hollow ZnO microspheres grown at 250 °C, suggesting synergistic effects of surface morphologies on optical nonlinearities.