Insight into Crystalline Structure and Physicochemical Properties of Quartz-Carbon Ore

: Composites made from carbon and nanominerals show great potential for thermal phase change materials, environmental water treatment, and biomass conversion. In 2019, a micro and nano-quartz-carbon ore was discovered in Feng-cheng City, Jiangxi Province. The study of the structural and physicochemical changes of quartz-carbon ore (QZC) during calcination is essential for the preparation of QZC-based composites and to broaden their application areas. Firstly, the SiO 2 crystal structure evolution of QZC during calcination was investigated using in-situ X-ray diffraction (XRD), 29 Si magic-angle sample spinning nuclear magnetic resonance (MAS NMR), and Fourier transform infrared FTIR spectroscopy. Then, the changes in carbon during calcination were investigated using Raman spectroscopy, 13 C MAS NMR, and X-ray photoelectron spectroscopy (XPS). In addition, changes in the QZC morphology were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Finally, the evolution of the physicochemical properties of QZC during calcination was revealed using thermogravimetric (TG), Brunauer–Emmet– Teller (BET), resistivity, thermal conductivity, and zeta potential techniques.


Introduction
Over the past decades, nanominerals have attracted considerable scientific interest due to their unique electronic and physical properties [1][2][3].They have broad application prospects concerning energy storage and conversion [4,5], biological therapy [6], and environmental restoration [7].Carbon materials have been widely studied and applied for their excellent thermodynamic properties, chemical stability, high specific surface area, high development, and good biocompatibility [8].In recent years, the synergistic preparation of carbon/nanomineral composites from nanomineral and carbon materials has been widely studied [9].Zhao et al. prepared carbon-coated aluminosilicate nanosheets with graded porosity using sucrose as a carbon source and kaolinite as a nanomineral [10].They further loaded stearic acid to develop a composite phase change material with photothermal conversion and thermal energy storage capabilities.Hao et al. prepared graphene oxide/montmorillonite composite aerogels for the removal of planar hydrated copper ions from complex wastewater systems, and the addition of montmorillonite can improve the adsorption performance of graphene oxide-based aerogels and reduce the cost [11].Binder-free continuous films of mesoporous carbon materials were synthesized on graphite collectors using ordered mesoporous silica films as hard templates; the synthesized films with excellent performance in terms of specific capacitance, rate performance, and electrochemical stability can be used as electrodes in microcapacitors [12].Composites combined with carbon and nanominerals show great potential for thermal phase change materials, environmental water treatment, and biomass conversion [13][14][15].However, the preparation of functional carbon/nanomineral composites by the addition of carbon materials to nanominerals often has the disadvantages of complicated and expensive processes.Therefore, natural carbon-containing nanominerals are critical for resolving the aforementioned issues.
In 2019, micro and nano-quartz-carbon ore was discovered in Feng-cheng City, Jiangxi Province [16].The resource reserves of this deposit are large-scale.Tang et al. studied the process mineralogy of quartz-carbon ore [17].After the ore mineral processing separation and purification tests, mesoporous silicon, mesoporous carbon, silica, nano-silica powder, and other materials can be obtained, and their industrial value is very high [16].In addition, little has been reported on the crystal structure and physicochemical properties of QZC.Therefore, the systematic study of the crystal structure, morphology, and surface physicochemical properties of QZC is of great theoretical significance for the realization of the functionalized design of QZC.
Understanding the structural and compositional evolution of QZC during gradual calcination in different atmospheres at high temperatures is essential to facilitate its application in catalysts, adsorbents, and phase change materials for thermal storage.This study investigates the thermal stability of QZC using thermogravimetry/differential scanning calorimetry (TG/DSC).It tracks the structural changes in QZC in real time during thermal treatment via in-situ X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FTIR).Furthermore, the physicochemical properties of minerals at different temperatures were systematically characterized using the Brunauer-Emmet-Teller (BET), laser particle size analyzer, zeta potential, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques, with the goal of providing a theoretical foundation for studying calcined QZC in composite materials, with the aim of laying the groundwork for the full utilization of the QZC and synthetic QZC composites, as well as for expanding the direction of applications.

Materials
The ore sample studied in this paper came from a drill hole in Fengcheng, Jiangxi Province, China (Figure S1).It comprised a stable black powder, which could not be ignited, was less dense than water, and was mainly composed of quartz, carbon, and other impurities.For testing and research purposes, the ore sample was ground and mixed, the QZC was sieved through an 80 mesh sieve, and the sieve offsets were dried in an oven at 50 • C for 24 h to obtain QZC.Table S1 shows the sample oxides' chemical composition and carbon content analyzed by an X-ray fluorescence (XRF) spectrometer and total organic carbon analyzer (TOC).

Preparation of QZC-A and QZC-N
A series of calcined silica carbonite samples were obtained by heating the QZC to the specified temperatures (from 100 to 1000 • C).QZC calcined under different atmospheres, air, and nitrogen (N 2 ), were labeled as QZC-A and QZC-N, respectively.The heating rate was 5 • C/min, held for 120 min after reaching the target temperature, then cooled naturally.The QZC becomes less malleable after heat treatment.The QZC and stearic acid (SA) were uniformly mixed using solvent evaporation, and the QZC mixture was pressed into small disc-shaped pieces to measure thermal conductivity.

Characterization
The chemical composition of the QZC was examined using a wavelength dispersive X-ray fluorescence spectrometer (XRF, PANalytical Axios, Amsterdam, the Netherlands).Determination of the total carbon (TC) values of QZC was performed using a total organic carbon analyzer (elementary vario TOC select, Frankfurt, Germany).X-ray diffraction (D8 ADVANCE, Bruker Corp., Saarbrucken, Germany) was used to study the evolution of the crystal structure and phase composition of the QZC samples after treatment with different temperatures and atmospheres.FTIR spectra were obtained by an FTIR spectrometer (BRUKER Tensor II, Karlsruhe, Germany) over a wavelength range of 4000-400 cm −1 .Analysis of changes in the local chemical environment and structure of H, C, and Si in the sample was conducted using solid-state NMR Popper NMR (ADVANCE III 400 WB, Saarbrucken, Germany).Sample surface characterization and carbon valence were characterized via X-ray photoelectron spectroscopy (ESCALAB Xi+, Massachusetts, MA, USA) using an Al Kα monochromator X-ray source.Changes in the chemical bonding environment led to important changes in photoelectron energy, which allowed chemical information to be obtained.C1s binding energy was 284.8 eV and was the reference for all measurements.Raman is the most efficient method for examining the structure of carbon without harming the substance since it is the fingerprint spectrum of the substance.The graphitization degree of the QZC was studied using a Raman spectrometer (LabRAM HR Evolution, Paris, France) at a 325 nm excitation wavelength.
The microstructure of the samples was investigated by scanning electron microscopy (SEM, ZEISS SIGMA 300, Oberkochen, Germany) with an energy dispersive (EDS) X-ray spectroscopy and transmission electron microscopy (TEM, JEOL JEM-2100F, Tokyo, Japan).Thermogravimetric and differential scanning calorimetric studies (TG/DSC, NETZSCH STA 449F3, Selb, Germany) were carried out to determine the thermal stability of raw QZC at a heating rate of 10 • C/min from 30 to 1000 • C. The specific surface area and the pore size distributions of the supporting materials were measured according to the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods using a nitrogen adsorption apparatus (ASAP 2020 Plus, Micromeritics, Norcross, GA, USA) at 77 K.The zeta potential of the samples was tested using a zeta potential analyzer (Brookhaven/90Plus PALS, Malvern, PA, USA) in the pH range of 1-12.The pH of the system was adjusted with 0.1 mol/L HCl or NaOH solution, respectively, using KCl as the electrolyte.A thermal conductivity meter (XIATECH TC3100, Xi'an, China) was used to characterize the pattern of changes in the thermal conductivity of the samples during crystal structure modulation and compositional changes.

Structural Characterization of Silicon and Carbon in QZC
Changes in the mineral crystal structure and physical phase during heat treatment were tracked in real-time.In-situ XRD with air atmosphere was performed to determine the relevant effects of temperature on the QZC structure and phase.Figure 1a shows the in-situ XRD spectra of the QZC during the heat treatment under the air atmosphere.The silica structure in the QZC is stable and highly crystalline, and there are no major changes in the distinctive peaks during the heat treatment process.After magnified observation of the characteristic peaks, it can be seen that the SiO 2 peak shifts towards a large angle after 550 • C, the cell parameters become larger, and the lattice becomes larger, transforming from low-temperature quartz to high-temperature quartz.As an example, the characteristic peak of the (101) crystal surface at 2θ = 26-28 • (Figure 1b).Meanwhile, the value of d (100) gradually increased from 4.25 nm to a maximum of 4.29 nm at 550 • C and then gradually decreased to 4.28 nm (Figure S2).In order to further explore the evolution of the local chemical environment of Si atoms in the QZC after heat treatment [18], NMR tests were performed on the QZC, QZC400-N, QZC600-N, and QZC800-N samples.The 29 Si spectra of sample QZC show symmetrical signal spikes at −91.90 ppm and −107.94ppm, corresponding to the typical Q 3 and Q 4 structures of the Si atoms in the QZC (Figure 1c).The Q 4 structure, i.e., Si atoms on [SiO 4 ] tetrahedra attached to four other equivalent Si-O tetrahedra [19], the sharp 29 Si NMR signals reflect the highly ordered, crystalline nature of the precursor [20].As the calcination temperature increased, the NMR chemical shifts corresponding to Q 4 of QZC400-N, QZC600-N, and QZC800-N shifted from the original −107.94ppm to 108.02, 108.01 and 108.15 ppm, respectively.The weakening and disappearance of the resonance peaks of the corresponding Q 3 structures of samples QZC600-N and QZC800-N and the broadening of the resonance peaks of Q 4 indicate a change in the bond lengths, bond angles, and cation-oxygen bond strengths of the QZC.The lower polymeric silica in Q 3 is converted to higher polymeric silica in Q 4 .
During the heat treatment process, the silica phase and coordination in the QZC undergo changes, but its crystallinity remains stable and almost unchanged.This property makes it suitable for high-temperature stabilization and fire-retardant materials.The relative crystallinity curve from Figure S3 shows that the crystallinity index of the QZC remains relatively stable, with slight variations above and below 100%.However, there is a direct drop in crystallinity to 88.5% at 300 • C, which is attributed to the removal of surface hydroxyl groups (−OH) from the QZC.This removal does not affect the SiO 2 crystallinity index.The XRD analysis does not reflect the presence of carbon peaks in the QZC, and the XRD patterns of the samples remain unchanged after heat treatment in both the air and N 2 atmosphere (Figure S4).Additionally, the crystallinity index of the QZC at 600 • C remained largely unchanged, indicating that the carbon in the QZC was amorphous.The βcosθ~sinθ fit lines for the heat-treated QZC are almost identical straight lines with very similar slopes (Figure 1d), and the crystal structure is stable and unchanged [21].
The FTIR technique was utilized to investigate the changing pattern of the groups on the surface of the QZC during the heat treatment process.The presence of a large number of (−OH) on the surface of the QZC can be seen in Figure 1e.The characteristic absorption peaks of (−OH) stretching vibrations appear in the range of 4000-3500 cm −1 , with two strong absorption peaks at wave numbers 3618.21cm −1 and 3687.04 cm −1 , respectively, and are attributed to the (−OH) within the QZC, formed by the stretching vibrations of the inner (−OH) and the inner surface (−OH), respectively [22].The inner hydroxyl axis is distributed almost parallel to the layer and, therefore, has a lower frequency.Compared to the QZC, the hydroxyl absorption peaks of QZC500-A at these two sites disappear [23].A single characteristic absorption peak was observed at 1567.89 cm −1 , which corresponds to the stretching vibration of the carbon-carbon bond, as confirmed by NMR spectroscopy [24].The carbon-carbon absorption peak at QZC600-A disappears due to the reaction of carbon with oxygen at high temperatures.After calcination under a nitrogen atmosphere, the stretching vibration of the carbon-carbon bond in QZC did not disappear, and this is the main difference between the FTIR spectra of QZC-A and QZC-N (Figure 1f).Five characteristic absorption peaks were identified in the range 400-800 cm −1 .The double peaks at 440.88 cm −1 and 510.10 cm −1 were Si-O-Si bending vibration absorption peaks, and the single characteristic absorption peak at 691.97 cm −1 was a Si-O-Si stretching vibration absorption peak [25].The Si-O-Si symmetric stretching vibration frequency of crystalline SiO 2 splits and is located as a double peak at 774.26 cm −1 and 792.57cm −1 [26].In contrast, the amorphous SiO 2 symmetric stretching vibration frequency is a single peak located at around 800 cm −1 , so based on the shape of the symmetric stretching vibration absorption peak, the QZC can be judged to be crystalline silica.The single characteristic absorption peak at 911.77 cm −1 is the −OH oscillating vibrational band and disappears at QZC500, corresponding to the presence of two absorption peaks at 3618.21 cm −1 and 3687.04 cm −1 .The Si-O-Si anti-symmetric stretching vibration absorption peaks in the silica-oxygen tetrahedra are at 1027.25 cm −1 and 1004.96cm −1 , where QZC500-A shows a blue shift, indicating an enhanced and stable Si-O-Si bond compared to the QZC.
QZC is mainly composed of SiO 2 and amorphous carbon.The alterations in silicon's crystal structure and coordination, as well as the functional groups, are revealed above.The characteristics of carbon matter in physics will then be revealed using Raman, 13 C NMR, and XPS.All samples show two broad peaks at 1345 cm −1 and 1580 cm −1 , corresponding to the D and G bands, with carbon defects estimated by the relative intensity ratio (I D /I G ) [27,28].The I D /I G values for QZC, QZC600-N, and QZC800-N are 1.02, 1.04, and 1.06, respectively, gradually increasing with increasing charring temperature (Figure 2a), indicating an increase in defect carbon and a decrease or no change in graphite carbon [29,30].The carbon-carbon double bond absorption peak at QZC800-N starts to weaken (Figure 1f), the carbon-carbon double bond starts to decrease, and the carbon-carbon double bond corresponds to the carbon hybridization mode of sp 2 hybridization.Figure 1f corresponds to the results of the data in Figure 2a.
The carbon-carbon double bond in the QZC is represented by a symmetric signal spike chemically shifted at 120.15 ppm in the 13 C NMR spectrum (Figure 2b).As the calcination temperature rises, the resonance peaks for QZC400-N, QZC600-N, and QZC800-N shift to 117.57, 116.96, and 108.32 ppm, respectively.The resonance peaks progressively expanded, and the intensity of QZC800-N declined dramatically, indicating that the carbon-carbon double bond was reduced and the C hybridization mode corresponding to the carbon-carbon double bond was sp 2 , consistent with the Raman results.O1s, C1s, Si2s, and Si2p were all detected in the QZC at different carbonization temperatures with binding energies of 528, 285, 154, and 103 eV, respectively (Figure 2c).To illustrate the structural evolution of elemental carbon further, we compared the high-resolution spectra of C1s of QZC at different calcination temperatures.Four diffraction peaks were present at binding energies of 284.80 eV, 285.20 eV, 285.80 eV, and 289.10 eV for all samples, corresponding to sp 2 -bound carbon(sp 2 -C), sp 3 -bound carbon(sp 3 -C), C-OH, and −COOH, respectively [13,31,32] (Figure 2d-f).Therefore, the results of the C1s high-resolution spectra show that the relative intensity of the sp 3 -bound carbon(sp 3 -C) increases with increasing carbonization temperature at 285.40 eV, with relative intensities of 25,277.76eV, 26,194.96eV, and 26,634.67eV, respec-tively, indicating an improvement in the crystal structure of the carbon in the QZC.Raman, 13 C NMR, and XPS results all indicate that as the calcination temperature increases, the defective carbon content rises, favoring a large number of adsorption sites for the applied material.The increase in defective carbon in QZC by calcination facilitates the preparation of carbon-based defective materials for applications in the direction of electrocatalysis, lithium-sulfur batteries, and energy storage.

Micromorphological Analysis
The color of the QZC varies throughout calcination, with a dramatic shift from black to pinkish white at 600 • C, attributed to the decomposition of its amorphous carbon and a transition to pure white at 1000 • C (Figure S5).It can be observed that the QZC is in a lamellar structure with tiny irregularly shaped crystals, and the original mineral grain size is in the range of tens of nanometers to about 1 micron in the micro-nano structure (Figures 3 and S6).Silicon and carbon exist together without a distribution pattern (Figures 3 and S7).After calcination at high temperatures, the QZC dehydroxylation appears as slabbing, and the particle size becomes larger (Figure S6).Even when heated to 1000 • C, the quartz-carbon ore retains an excellent lamellar structure, indicating its thermal resilience.Natural QZC crystal particles are made up of micro and nanosheets with tiny diameters, thin thicknesses, and great crystallinity.After heat treatment, the flakes' lamellar structure stays unaltered.The amorphous carbon and SiO 2 crystal structures are visible in Figure 4.The FTIR scan reveals that the heat-treated QZC retains a strong crystal structure, exhibiting its high thermal stability, which is consistent with the XRD results.

Physico-Chemical Properties of Quartz-Carbon Ore
The above experimental test results show the crystal structure model of QZC and the changes in the physical phase, crystal structure, functional groups, and quartz-carbon during heat treatment to further explore the physicochemical properties of QZC using TG-DSC-DTG, BET, resistivity and thermal conductivity, and zeta potential.They were evaluated for thermal stability under air and N 2 atmospheres to reveal more about the carbon content and thermal transformation capabilities of the QZC.The TG-DSC-DTG curve for quartz-carbon ore under air atmosphere (Figure 5a) over the range of 20-1000 • C degrees can be divided into three phases.The first stage was from 20 to 157 • C with a QZC weight loss of 0.18% and a small valley of heat uptake at 81.2 • C, which was mainly attributed to the removal of adsorbed water from the QZC and the release of volatile compounds from the mineral sample; A second stage of 157-426 • C was for the removal of interlayer water (structure water).The third stage was 396-700 • C with a weight loss of 13.39%, indicating the complete decomposition of the fixed carbon in the QZC, which decomposes at a higher temperature in the QZC than in coal because of the silicon-covered carbon structure in the QZC and the protection of the carbon by the silicon.The exothermic peak at this stage is 670 • C, with an exothermic peak at 573.2 • C corresponding to the crystalline transition temperature of quartz for the transition from α to β quartz.The TG-DSC-DTG curve under an N 2 atmosphere (Figure 5b) can likewise be divided into three stages.The first stage is from 20-162 • C, where the QZC loses 0.28% of its weight, with a small valley of heat absorption at 81.4 • C, which is mainly attributable to the removal of water adsorbed by QZC.A second stage of 162-420 • C was for the removal of interlayer water (structure water).The third stage is 396-1000 • C with a weight loss of 1.89%, which is mainly the decomposition of organic carbon and may contain the removal of humic acids.A peak in 573.1 • C appears as a transition from α to β quartz [33].Ordinary SiO2 materials have very low electrical conductivity and are generally regarded as insulators, so they can generally be used to produce high-frequency insulators.The carbon in the QZC is a crystal structure formed by sp 2 hybridized carbon atoms in a honeycomb arrangement.In contrast, the crystal structure of [SiO4] tetrahedra and sp 2 hybridized carbon atoms in the QZC crystal alters the electron transfer path within the SiO2 crystal in the QZC.It has an impact on the electrical conductivity of the QZC.The resistivity in quartz-carbon ore gradually decreased from 161.14 Ω•cm to 19.39 Ω•cm under 2-20 Mpa (Figure 5e), and after calcination under air atmosphere, the carbon in the crystal of QZC600-A was missing, which considerably blocked the electron transfer path in the crystal, and the resistivity directly increased to 233.23-629.24MΩ•cm, compared with QZC600-A, the other volatile impurities in the sample QZC1000-A were removed entirely and the resistivity increased slightly, which is expected to become a functional anti-static filler for industrial paints.
The thermal conductivity of the QZC after calcination under an air atmosphere, de- The pore organization structure of the material is related to the shape of the adsorption equilibrium isotherm; according to IUPAC classification, the N 2 adsorption/desorption isotherm curves of the calcined samples under both air and N 2 atmospheres are of type IV.The hysteresis line corresponds to the mixing of H3 and H4 (Figure S9); there is no obvious saturation adsorption plateau, the pore structure is more unevenly distributed, and the QZC lamellar particles accumulate to form cleavage pores at a lower relative.The adsorption that occurred at lower relative pressures P/P 0 was mainly monomolecular layer adsorption followed by multilayer adsorption, with pressures P/P 0 larger than 0.9 being sufficient for capillary coalescence to occur and the adsorption isotherm showing a sudden surge.According to the pore size distribution graphs of the samples calculated using the BJH method (suitable for mesopores), the raw samples are concentrated at 3.8 nm (Figure 5c,d), and the disappearance of the peak at 3.8 nm in the pore size distribution curve after calcination of the samples in air atmosphere up to 600 • C, as well as the absence of a hysteresis loop, indicates a collapse of the pore structure.Compared to the air atmosphere calcined samples, for the QZC after calcination under an N 2 atmosphere, the isothermal curves and pore size distribution curves did not change much within the temperature range of 400-1000 • C.This indicates that the mesopores in the sample are mainly formed by carbon material and are not related to silica [34,35].The porous structure influenced by silicon and carbon in the QZC can be loaded with catalysts for catalysis and environmental applications such as air purification, water purification, self-purification, sterilization, and deodorization.
Ordinary SiO 2 materials have very low electrical conductivity and are generally regarded as insulators, so they can generally be used to produce high-frequency insulators.The carbon in the QZC is a crystal structure formed by sp 2 hybridized carbon atoms in a honeycomb arrangement.In contrast, the crystal structure of [SiO 4 ] tetrahedra and sp 2 hybridized carbon atoms in the QZC crystal alters the electron transfer path within the SiO 2 crystal in the QZC.It has an impact on the electrical conductivity of the QZC.The resistivity in quartz-carbon ore gradually decreased from 161.14 Ω•cm to 19.39 Ω•cm under 2-20 Mpa (Figure 5e), and after calcination under air atmosphere, the carbon in the crystal of QZC600-A was missing, which considerably blocked the electron transfer path in the crystal, and the resistivity directly increased to 233.23-629.24MΩ•cm, compared with QZC600-A, the other volatile impurities in the sample QZC1000-A were removed entirely and the resistivity increased slightly, which is expected to become a functional anti-static filler for industrial paints.
The thermal conductivity of the QZC after calcination under an air atmosphere, decreases with the absence of carbon (Figure 5f).Heat treatment allows for the modification of the crystal structure and composition of quartz-carbon ore, which has a significant impact on their thermal conductivity.As a result, the implant's crystal structure, composition, and particle size gradually decrease from 0.121 W•m −1 •K −1 to 0.094 W•m −1 •K −1 .The decrease in thermal conductivity observed in sample QZC600-A can be attributed to the carbon loss that occurred during the heat treatment of quartz-carbon ore, leading to a modification in the crystal structure of the sample.The crystal structure of the quartz-carbon ore experiences an increase in bond lengths and bond angles in the [SiO 4 ] tetrahedra, as well as the elimination of carbon-carbon double bonds.These changes result in a significant number of thermally excited defects.The presence of these defects causes severe phonon-defect scattering, which hinders the propagation of phonons, shortens their average free range, and ultimately reduces the thermal conductivity of QZC.Compared to QZC600-A, QZC1000-A is completely calcined, with the disappearance of volatile fraction, and the thermal conductivity is slightly reduced from 0.103 W•m −1 •K −1 to 0.094 W•m −1 •K −1 , mainly due to the effect of particle size distribution.The QZC1000-A particle size is larger compared to QZC600-A, and the non-homogeneity is increased, producing secondary pores, which increases the interfacial area of the QZC, enhancing the phonon scattering effect and reducing the thermal conductivity of the QZC [36,37].Consideration can be given to separating the silicon and carbon in the QZC using some physicochemical methods and using the carbon to make materials with high thermal conductivity, for example, for making heat storage materials, which increase the channels for heat transfer through the increase of defective carbon after heat treatment.
The surface potential of the quartz-carbon ore calcined under different temperatures and atmospheres changes significantly, according to the zeta potential function results (Figure 5g,h).The raw ore and QZC400-A appear to have an isoelectric point in an acidic environment, 4.10 and 3.16, respectively, and the potential values are negative after 600 • C and increase with pH.This indicates that the potential of the QZC is influenced by the carbon material in the sample, with the carbon material carrying a positive point in an acidic environment and the carbon material carrying a negative charge after calcination and decomposition due to the dehydroxylation of the QZC.After calcination, the potential of the QZC shows a negative value and increases, which can be used to treat positively charged pollutants, such as Methylene blue and Rhodamine B.

Conclusions
In this study, the material composition, morphology, crystal structure, and physicochemical properties of quartz-carbon ore were first studied.The quartz-carbon ore consists of well-crystallized SiO 2 and amorphous carbon; SiO 2 in the QZC contains hydroxyl groups and has Q 4 and Q 3 structures, and its amorphous carbon is connected by carbon-carbon double bonds and contains hydroxyl and carboxyl groups.The interlocking pattern between SiO 2 and amorphous carbon appears through Si and C. Notably, the Si-C interlocking structure of the ore was proposed for the first time in conjunction with the formation process of the QZC.Next, the evolution of the crystal structure, morphology, and physical and chemical properties were systematically investigated by heat treatment of the ore under air and nitrogen atmospheres.The SiO 2 in the QZC is well crystalline, and the stable crystal structure after heat treatment was proven by the Si atomic coordination changes, and the transformation from lower polymeric Si in Q 3 to higher polymeric Si in Q 4 happens after 600 • C. The four characterization results from the XRD, 13 C NMR, Raman, and XPS correspond and demonstrate a reduction in carbon-carbon double bonds, an increase in defective carbon, and an increase in the relative strength of sp 3 hybridized carbon.TG, BET, resistivity, thermal conductivity, and zeta tests on samples of the ore after heat treatment under air and N 2 atmospheres subsequently concluded that the collapse of mesopores, the strength of resistivity, the high thermal conductivity, and the change in potential are all closely related to the carbon in the ore.Our results systematically confirm the structure evolution of the QZC after heat treatment under different atmospheres, providing a theoretical basis for the preparation of functional QZC composites and a direction for high-value applications.

Figure 1 .
Figure 1.(a) In-situ XRD patterns, (b) in-situ XRD peak at around 26.5 • , (c) 29 Si MAS NMR spectra of the QZC, and calcined samples at different temperatures, (d) βcosθ~sinθ curves; FTIR spectra of the QZC calcined at different temperatures (e) under air and (f) under N 2 atmospheres.

Minerals 2023 , 13 Figure 5 .
Figure 5. TG-DSC curves of pristine QZC (a) under air and (b) under N2 atmospheres; BJH pore size distribution curves of pristine QZC and calcined samples at different temperatures (c) under air and (d) under N2 atmospheres; (e) resistivity of the sample; (f) thermal conductivities of QZC, QZC600-A, and QZC1000-A; zeta potential of pristine QZC and calcined samples at different temperatures (g) under air and (h) under N2 atmospheres.

Figure 5 .
Figure 5. TG-DSC curves of pristine QZC (a) under air and (b) under N 2 atmospheres; BJH pore size distribution curves of pristine QZC and calcined samples at different temperatures (c) under air and (d) under N 2 atmospheres; (e) resistivity of the sample; (f) thermal conductivities of QZC, QZC600-A, and QZC1000-A; zeta potential of pristine QZC and calcined samples at different temperatures (g) under air and (h) under N 2 atmospheres.

Funding:
This work was supported by the National Key R&D Program of China (2022YFC2904804), the CUG Scholar Scientific Research Funds at China University of Geosciences (Wuhan) (2019152), the Fundamental Research Funds for the Central Universities at China University of Geosciences (Wuhan), and the National Science Fund for Distinguished Young Scholars (51225403).