Hydrothermal-assisted Sol-gel Method Research Articles

Surface engineering of Li3V2(PO4)3-based cathode materials with enhanced performance for lithium-ion batteries working in a wide temperature range

Operating at extreme temperatures is the biggest challenge for lithium-ion batteries (LIBs) in practical applications, as both the capacity and cycling stability of LIBs are largely decreased due to the sluggish reaction kinetics of the cathodes. Therefore, developing suitable cathode materials is the key point to tackling this challenge. Lithium vanadium phosphate [Li3V2(PO4)3, LVP] is a promising cathode with good features of a high working voltage, high intrinsic ionic diffusion coefficiency, and stable olivine structure in a wide temperature range, although it is perplexed by the low electronic conductivity. To tackle this issue, a series of nitrogen-doped carbon network (NC) coated LVP composites were synthesized using a hydrothermal-assisted sol-gel method. Among them, the LVP@NC-0.8 sample exhibited a remarkable tolerance at a high charging cutoff voltage of 4.8 V in a wide temperature range. Full cells of LVP@NC-0.8||graphite exhibited superior performance at different current rates. Moreover, the reaction mechanism of the LVP@NC-0.8 electrode was proved by in-situ X-ray diffraction technique, demonstrating that temperature was a critical factor that contributed to the sluggish phase transformation with high voltage hysteresis at low temperature and severe crystal structure distortion at high temperature. Theoretical calculations further demonstrated the superiority of the NC for high electronic conductivity and reduced lithium transportation barriers. The enhanced electrochemical performances of LVP-based cathode materials have provided the possible application of LIBs in a wide temperature range.

N-doped carbon decorated Na3V2(PO4)3@NC composite derived from melamine as cathode material for high-rate and ultralong-life sodium-ion batteries

Sodium superionic conductor (NASICON) Na3V2(PO4)3 (NVP) is one of the most promising cathode materials for Sodium ion batteries (SIBs). However, its low electronic conductivity makes the cycle and rate performance less ideal. Increasing the electronic conductivity of NVP by carbon coating has been more and more confirmed, especially for N-doped carbon. Here, in-situ melamine-derived N-doped carbon-coated Na3V2(PO4)3@NC (NVP@NC) by hydrothermal-assisted sol-gel method is prepared. The introduction of N has no effect on the original NASICON structure of NVP@C, but the melamine addition amount affected the intensity of the diffraction peak from different NVP@NC samples. The NVP@NC shows superior cycling and rate performance. In the NVP@NC-2 sample with nC3N6H6/nNVP = 2, its discharge capacity maintains 106.82 mAh·g−1 at the 500th cycle at 0.2 C. The reversible capacities at 10 and 20 C are 90.5 and 85.0 mAh·g−1 with capacity retention of 81.2% and 76.3%, respectively. The zero-band gap of NVP@NC-2 through first-principles calculations means the ionic conductivity of NVP@C is greatly enhanced after N doping. The addition of the N element to the carbon layer contributes a pair of lone pairs of electrons to the matrix carbon and introduces certain active sites and defects. The reason for the improved electrochemical performance is that the N-doped carbon layer (NC) enables the expansion and deformation of the crystal structure to be controlled, increasing the Na+ diffusion coefficient and the electrical conductivity of NVP.

Stable cycling performance of lituium-doping Na3−xLixV2(PO4)3/C (0 ≤ x ≤ 0.4) cathode materials by Na-site manipulation strategy

Na3V2(PO4)3 (NVP) has become a hot material in the research field of sodium-ion batteries (SIBs) as a result of its unique structural advantages. Unfortunately, the poor electronic conductivity and ion diffusion ability fundamentally limit the practical development of NVP. Considering the above defects, a series of Li+ doped Na3−xLixV2(PO4)3/C cathode materials for SIBs are synthesized through hydrothermal assisted sol–gel method. The cell volume steadily decline with the raise of Li+ doping amount, which is consistent with the usual doping effect. Moreover, with the increase of lithium doping amount, Li+ preferentially occupies Na(2) site and then occupies Na(1) site. Through the first principles calculation, it is clear that the introduction of Li+ can significantly reinforce the conductivity of the material system and diminish the electron localization phenomenon. The analysis of (116) crystal plane by TEM shows that Li doping will reduce the interplanar spacing. The change of V valence during the charge–discharge process of Na2.8Li0.2V2(PO4)3/C is consistent with that of NVP by V element XANES characterization. There is no conventional phase transition phenomenon in the ex-situ XRD high-voltage charging state. The above facts indicate that lithium doping obtains a stable solid solution NVP. The electrochemical test results show that Na2.8Li0.2V2(PO4)3/C can provide an amazing reversible capacity of 116.9 mAh/g (theoretical capacity of 117 mAh/g) and capacity retention rate of 99.82 % after 500 cycles. GITT results show that Li+ can significantly increase the Na+ diffusion coefficient of the material. Such excellent electrochemical performance is attributed to the fact that the doping of Li+ activates the activity of Na+ in Na(2) site and improves the reaction efficiency.

The effect of rare earth (Er, Yb) element doping on the crystallization of Y2Ti2O7 pyrochlore nanoparticles developed by hydrothermal-assisted-sol-gel method

Given the required properties for an active medium producing luminescent materials, two host matrices were selected for this study: titanium oxide (TiO2) and yttrium oxide (Y2O3) due to its desired properties. In this paper, Doped and undoped YTO (Y2O3–TiO2) nanopowders with Erbium (Er) and/or Ytterbium (Yb) has been successfully fabricated by hydrothermal-assisted sol-gel method using supercritical drying of ethanol and annealing at 900, 1000, 1300 and 1600 ​°C for 1 ​h. The nanoparticles (NPs) were prepared from organometallic precursors. The aim of this study is to obtain well-crystallized pyrochlore (Y2Ti2O7) phase nanoparticles. The XRD analysis shows the crystallization of pyrochlore phase at 1600 ​°C for the pure powder and from 900 ​°C for the doped powders. The crystallization of the pyrochlore phase was improved after doping with Er and/or Yb and the Ytterbium dopant exhibits a significant influence on the crystallization of Y2Ti2O7 phase. The size of nanoparticles was estimated between 19 and 60 and about 32 ​nm using TEM. Observations using SEM were carried out in order to study the morphology of the nanopowders. The images show fine nanoparticles with spherical form and large agglomerates rich in yttrium. The optical properties are improved after the thermal treatment of the powders and down conversion phenomenon has been observed for the Er-doped NPs.

Preparation of Li3V2(PO4)3 as cathode material for aqueous zinc ion batteries by a hydrothermal assisted sol-gel method and its properties.

To alleviate the depletion of lithium resources and improve battery capacity and rate capacity, the development of aqueous zinc-ion batteries (AZIBs) is crucial. The open channels monoclinic structure Li3V2(PO4)3 is conducive to the transfer and diffusion of guest ions, making it a promising cathode material for AZIBs. Therefore, in this study, nanoneedles and particles Li3V2(PO4)3 cathode materials for AZIBs were prepared by a hydrothermal assisted sol-gel method, and the effect of synthesized pH values was studied. XRD results show that all samples had the monoclinic structure, and the Li3V2(PO4)3 sample prepared at pH = 7 exhibits (LVP-pH7) the highest peak tips and narrowest peak widths. SEM images demonstrate that all samples have the morphology character of randomly oriented needles and irregular particles, with the LVP-pH7 sample having more needle-like particles that contribute to ion diffusion. EDS results show uniform distribution of P, V, and O elements in the LVP-pH7 sample, and no obvious aggregation phenomenon is observed. Electrochemical tests have shown that the LVP-pH7 sample exhibits excellent cycling performance (97.37% after 50 cycles at 200 mA g-1) and rate ability compared to other samples. The CV test results showed that compared with other samples, the LVP-pH7 sample had the most excellent ionic diffusion coefficient (2.44 × 10-12 cm2 s-1). Additionally, the Rct of LVP-pH7 is the lowest (319.83 Ω) according to the findings of EIS and Nyquist plot fitting, showing a decreased charge transfer resistance and raising the kinetics of the reaction.

Preparation of amorphous ZrO2 powders by hydrothermal-assisted sol-gel method

Amorphous ZrO2 exhibited broad application prospect as support materials. Herein, amorphous ZrO2 powders were prepared by a novel hydrothermal-assisted sol-gel route using zirconium oxychloride (ZrOCl2⋅8H2O) as zirconium source and ammonia water (NH3⋅H2O) as precipitant. The effects of pH, zirconium source concentration, and hydrothermal treatment on the properties of ZrO2 powders were investigated. The phase structure and microstructure were also investigated. The proprieties of the powders obtained from hydrothermal-assisted sol-gel were compared with those of conventional sol-gel method. The particle size of sample obtained from hydrothermal-assisted sol-gel (80 nm) was smaller than that of conventional sol-gel (210 nm). And the purity was also higher (99.95 vs 98.56 wt%). These results demonstrated that the obtained ZrO2 powders have amorphous structure, uniform and small particle size, rough and loose surface, and high purity.

Preparation and infiltration of NASICON-type solid electrolytes with microporous channels

A lithium-ion conductor with microporous channels (p-LATP) was prepared by using templates from a hydrothermal-assisted sol-gel method, and the as-prepared p-LATP was infiltrated to obtain p-LATP and d-LATPs composites in this work. SEM photos showed that the morphologies of p-LATP, d-LATP, and p-LATP and d-LATP composites were quite similar. XRD analysis showed that the crystallographic structures were also similar. TEM examinations revealed that microporous channels existed in the pure p-LATP and the p-LATP and d-LATP composites but not in the pure d-LATP. The total conductivities of the composites were higher than those of the pure p-LATP and pure d-LATP. The enhancement of the total conductivity of the composites was ascribed to the interaction of microporous channels and dense lithium-ion conducting areas. The promising results obtained in this work provide a new way to prepare solid lithium-ion conductors.

Effect of sol-gel derived TiO2 nanopowders on the mechanical and structural properties of a polymer matrix nanocomposites developed by vacuum-assisted resin transfer molding (VARTM)

In this study, the impact of adding TiO2 nanopowders prepared by hydrothermal-assisted sol-gel method on the mechanical properties of a polyester composite reinforced by glass fibers has been investigated. The nanocomposite was fabricated using vacuum-assisted resin transfer molding (VARTM) with TiO2 nanopowders amount ranging from 0 to 7.5 wt%. The obtained results have shown that, firstly, TiO2 nanopowders are formed of anatase structure with a nanometric size in the range of 10–12 nm. Secondly, the optimum amount of TiO2 nanopowders with enhanced properties of the nanocomposite was around 5 wt%. At optimal conditions and compared to unfilled composites, the microhardness increased from 15 to 21 Hv. This result is in good correlation with the tensile modulus, ultimate tensile strength (UTS) and strain to break (SB) which increased by 14%, 83% and 246%, respectively. Including high specific strength and modulus, good fatigue resistance, a these findings may have interesting industrial applications.

Temperature‐dependent Battery Performance of a Na3V2(PO4)2F3@MWCNT Cathode and In‐situ Heat Generation on Cycling

Excellent structural stability, high operating voltage, and high capacity have made Na3 V2 (PO4 )2 F3 a promising cathode material for sodium-ion batteries. However, high-temperature battery performances and heat generation measurements have not been systematically reported yet. Carbon-coated Na3 V2 (PO4 )2 F3 @MWCNT (multi-walled carbon nanotube) samples are fabricated by a hydrothermal-assisted sol-gel method and the electrochemical performances are evaluated at three different temperatures (25, 45, and 55 °C). The well-crystallized Na3 V2 (PO4 )2 F3 @MWCNT samples exhibit good cycling stability at both low and high temperatures; they deliver an initial discharge capacity of 120-125 mAhg-1 at a 1 C rate with a retention of 53 % capacity after 1,400 cycles with 99 % columbic efficiency. The half-cell delivers a capacity of 100 mAhg-1 even at a high rate of 10 C at room temperature. Furthermore, the Na3 V2 (PO4 )2 F3 @MWCNT samples show good long-term durability; the capacity loss is an average of 0.05 % per cycle at a 1 C rate at 55 °C. Furthermore, ionic diffusivity and charge transfer resistance are evaluated as functions of state of charge, and they explain the high electrochemical performance of the Na3 V2 (PO4 )2 F3 @MWCNT samples. In-situ heat generation measurements reveal reversible results upon cycling owing to the high structural stability of the material. Excellent electrochemical performances are also demonstrated in the full-cell configuration with hard carbon as well as antimony Sb/C anodes.

Synthesis of upconversion TiO2:Er3+-Yb3+ nanoparticles and deposition of thin films by spin coating technique

In this work, a simple, low temperature (T < 300 °C) procedure suitable to increase the efficiency of solar cell and optoelectronic devices through reducing the mismatch with solar spectrum in the infrared range is proposed. TiO2 co-doped with rare earth ions is a promising candidate for its use in optical field due to the possibility to expand the spectral absorption range. Here, pure and Er3+-Yb3+co-doped anatase-TiO2 nano-spherical particles (diameter < 50 nm) with high surface area (125.7 m2/g and 140.6 m2/g for the pure and co-doped, respectively), good crystallinity are prepared by hydrothermal-assisted sol-gel method, followed by their dispersion and deposition as thin films. The nanoparticles are characterized by studying their structural, morphology, surface chemical compositions and photoluminescent properties. From the dispersion study, results showed that the optimal conditions were obtained for co-doped TiO2 at operational pH = 3 and with 20 min as a suitable duration of ultrasonication. The co-doped TiO2 nanoparticles showed excellent upconversion properties (green and red emissions) at room temperature under 980 nm excitation. To extend this result towards optoelectronic and photonic applications, the upconversion nanoparticles are deposited at the surface of n-type (100) Si wafer using a spin-coating process. From scanning electron microscopy, it is observed that the entire surface of substrate is covered with a uniform film composed of compact arrangement of small nanoparticles with a good adhesion on Si surface, also the resulting 750 nm thick TiO2:Er–Yb film maintained the upconversion luminescence phenomena.

Porous Na3V2(PO4)3/C as cathode material for high-rate sodium-ion batteries by sacrificed template method

NASICON-type Na3V2(PO4)3 with a three-dimensional open framework structure has attracted wide attention, and it is regarded as one of the most promising cathode material for sodium-ion batteries. However, the low electronic conductivity restricts its charge–discharge capacity and electrochemical performance. With the purpose to solve this problem, polystyrene microspheres are applied in the preparation of cathode materials for sodium-ion batteries. Particular porous-structured Na3V2(PO4)3 composing of interlaced nanosheets is obtained samples by a simple hydrothermal-assisted sol–gel method via a self-sacrificed template (polystyrene microsphere). As expected, the as-prepared porous sample delivers a reversible capacity of 109.2 mAh g−1 at 0.2 C, an excellent rate performance (89.6 mAh g−1 at 50 C) and superior cyclic stability (retention of 94% over 500 cycles at 50 C). The outstanding rate and cyclic performance are attributed to its unique porous structure which is conducive to improve electron conductivity and facilitate the diffusion of sodium ions.

Recrystallization and coalescence kinetics of TiO2 and ZnO nano-catalysts towards enhanced photocatalytic activity and colloidal stability within slurry reactors

Advanced oxidation processes rely on the development of stable photocatalytic materials, offering specific band-gap attained upon reaching appropriate crystalline phases. A key research gap is related to the recrystallization of nano-catalysts and their impact on performance. This paper describes the systematic preparation of TiO2 and ZnO nanoparticles by hydrothermal-assisted sol-gel method followed by systematic calcination steps with the aim to shed light on the recrystallization process to engineer higher photocatalytic activity. Spherical anatase-TiO2 nanoparticles with a 20 nm diameter size present higher photocatalytic activity than 70 nm of ZnO NPs calcined at 500 °C. A photocatalytic yield of 84% within 30 min of irradiation for the degradation of model dyes was observed for the titania particles, which were also less sensitive to a gglomeration, a key challenge when designing slurry reactors. The variation in zeta potential of TiO2 and ZnO with pH exhibited isoelectric points (IEP) in aqueous media at 5.1 and 6.5, respectively, suggesting amphoteric behaviors while X ray photo-electron spectroscopy and diffusive reflectance spectroscopy data were used to characterize the changes in surface vacancies and the band gap of the materials. These data open the door to the development of advanced oxidation processes in complex industrial environments.

Optical, Magnetic, Ferroelectric Properties and Photocatalytic Activity of Bi2Fe4O9 Nanoparticles through a Hydrothermal Assisted Sol–Gel Method

Polycrystalline Bi2Fe4O9 nanoparticles were successfully prepared by a hydrothermal assisted sol-gel method. X-ray diffraction (XRD) data, Fourier transform infrared (FTIR) spectra, and Raman spectra reveal that Bi2Fe4O9 nanoparticles has orthorhombic mullite structure without other impurities such as Bi2O3, Fe3O4, BiFeO3, Fe2O3. Scanning electron microscopy (SEM) shows that the synthesized polycrystalline Bi2Fe4O9 particles have regular spherical shape and the average particle size of 50 nm. Optical properties of the Bi2Fe4O9 nanoparticles were studied by UV–Vis absorption spectroscopy, and the bandgap energy (Eg) value is found to be 1.75 eV. Magnetic characterization shows that the Bi2Fe4O9 nanoparticles exhibit a paramagnetic behavior at 300 K and undergo an antiferromagnetic transition at 190 K. Ferroelectric hysteresis loops with rounded corners at room temperature at 50 Hz are observed for the Bi2Fe4O9 nanoparticles due to the large electrical leakage. Photocatalytic experiments indicate that the Bi2Fe4O9 nanoparticles exhibit excellent photocatalytic activity and stability in degradation of methylene blue (MB) and methyl red (MR) dyes under visible light irradiation.

Electrical performance of fine-grained Y-TZP/TiC composites obtained through a hydrothermal-assisted sol-gel process

Y2O3-stabilized tetragonal ZrO2 polycrystal (Y-TZP) composites with various TiC contents were successfully synthesized via a modified hydrothermal-assisted sol-gel method. Fine precursor powders can be obtained with high crystallinity, nanoscale grain size and uniform morphology. SEM images of the ceramic products show that TiC particles are distributed homogeneously in the final Y-TZP matrix, and their average grain sizes are approximately 390–670 nm and 150–230 nm for the Y-TZP and TiC phases, respectively. A higher TiC volume fraction has a negative effect on the relative density and hardness but a significant positive influence on electrical conductivity. The electrical conductivity values are increased from 115 S/m to 1.23 × 105 S/m with TiC contents varying, demonstrating that the percolation threshold is approximately as low as 11.6 vol% for the samples, which is much lower than those of previous Y-TZP/TiC ceramics. The high electrical performance is probably due to the high D (the diameters of the insulating particles)/d (the diameters of conductive particles) ratio and submicron-sized grains.

Synthesis, Photoluminescence and Photocatalytic Activity of Tetragonal SnO2 Prepared by Hydrothermal Sol-Gel Method

Luminescent SnO2 material was synthesized by a hydrothermal assisted sol-gel method. X-ray powder diffraction analysis indicates that the as-synthesized SnO2 is a tetragonal phase and the calculated lattice parameters a and c are 0.474 and 0.318 nm, respectively. Scanning electron microscopy shows that the prepared tetragonal SnO2 particles have regular rhombic shape and are polydisperse without any agglomeration. Ultraviolet-visible absorption spectroscopy was used to study the light-absorbing properties and bandgap of tetragonal SnO2, and the value of bandgap is obtained to be 2.894 eV. The emission spectrum detected at λex = 230 nm showed two peaks located at 375 and 415 nm, the first having the strongest luminescence intensity. The fluorescence emission spectra also show that an emission peak at 510 nm is observed when the λex is 400 nm. Photocatalytic experiments indicate that the tetragonal SnO2 exhibits a strongly enhanced photocatalytic activity than commercial nano-SnO2 in photocatalytic degradation of various dyes under visible light irradiation. The photocatalytic mechanism is discussed on the basis of X-ray photoelectron spectroscopy (XPS) data, Fourier transform infrared (FTIR) spectra, electrochemical measurements and photocatalytic experiments results.

Low-temperature preparation of a N-TiO2/macroporous resin photocatalyst to degrade organic pollutants

Highly active TiO2 photocatalysts prepared at a low temperature are promising reagents to degrade organic pollutants. Moreover, the addition of macroporous resins should overcome the poor adsorption properties of TiO2. Here we prepared N-doped TiO2/macroporous resin composites at low temperatures using a hydrothermal-assisted sol–gel method. The results show that the composites have a spherical appearance, which is controlled by the macroporous resin. The composites exhibit high specific surface areas, and the microstructure can be tuned by the temperature. N can be doped into the TiO2 crystal by substitution of oxygen at a lower temperature. N-doped TiO2 particles are distributed on the surface with a dominant crystal form of anatase. The composite prepared at 200 °C gave the best performance for the photocatalytic degradation of rhodamine B, with removal efficiency of 74.8% following 240-min irradiation.

Phase evolution and chemical stability of the Nd2O3-ZrO2-SiO2 system synthesized by a novel hydrothermal-assisted sol-gel process

A hydrothermal-assisted sol-gel process, a novel method of combining both advantages of sol-gel and hydrothermal processes, was developed to synthesize dense Nd-doped ZrSiO4 ceramics with high Nd (surrogate for trivalent actinides) loading at low sintering temperature (1723 K) and short time (6 h). The evolutions of phase and microstructure of the obtained ceramics with the varying composition, sintering temperature and pH value were investigated. The chemical durability of the ceramics was also evaluated. The results show that the properties of ceramics strongly depend on sintering temperature and pH value. The acidic condition is beneficial to phase formation and densification of ZrSiO4 ceramics. It was found that the maximum immobilization capacity of Nd in the single-phase ZrSiO4 ceramics is highly dependent upon the synthesis method and sintering temperature. With decreasing sintering temperature, the maximum immobilization capacity increases. And the immobilization capacity of Nd in ZrSiO4 ceramics was found to be enhanced by the hydrothermal-assisted sol-gel method. Furthermore, the normalized release rate of Nd in Nd-doped ZrSiO4 ceramics decreases with increasing time and remains almost unchanged (∼10−4 g m-2 d-1) after 28 days, and the fractional release of Nd in all samples is about ∼10−5 wt%, exhibiting high chemical stability.

Enhanced electrochemical performance of Na3V2(PO4)2F3 for Na-ion batteries with nanostructure and carbon coating

Carbon-coating Na3V2(PO4)2F3 nanoparticles (NVPF@C NP) were prepared by a hydrothermal assisted sol–gel method and applied as cathode materials for Na-ion batteries. The as-prepared nanocomposites were composed of Na3V2(PO4)2F3 nanoparticles with a typical size of ~ 100 nm and an amorphous carbon layer with the thickness of ~ 5 nm. Cyclic voltammetry, rate and cycling, and electrochemical impedance spectroscopy tests were used to discuss the effect of carbon coating and nanostructure. Results display that the as-prepared NVPF@C NP demonstrates a higher rate capability and better long cycling performance compared with bare Na3V2(PO4)2F3 bulk (72 mA h g−1 at 10 C vs 39 mA h g−1 at 10 and 1 C capacity retention of 95% vs 88% after 50 cycles). The remarking electrode performance was attributed to the combination of nanostructure and carbon coating, which can provide short Na-ion diffusion distance and rapid electron migration.

Structural analysis of metal-doped (Mn, Fe, Co, Ni, Cu, Zn) calcium hydroxyapatite synthetized by a sol-gel microwave-assisted method

Abstract Incorporating metal ions into a calcium hydroxyapatite structure is a successful pathway to increase their physical, chemical and biological properties. The calcium hydroxyapatite was obtained by co-precipitation and a hydrothermal-assisted sol-gel method at a low temperature, using Ca(NO 3 ) 2 ·4H 2 O and (NH 4 ) 2 HPO 4 as sources of calcium and phosphorus. Metal ion (M + = Mn 2+ , Fe 3+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ ) incorporation was carried out in solutions of calcium hydroxyapatite and the corresponding nitrate salts. Hydroxyapatite powders doped with metal ions were characterized by X-ray diffraction and FTIR analysis to evaluate the structural and compositional changes. The only phase present in pure and doped calcium hydroxyapatite samples (M + = Mn 2+ , Fe 3+ , Ni 2+ ) was the hexagonal one. A Rietveld refinement showed that doping with these ions does not affect the volume of the hexagonal unit cell. Both hexagonal and monoclinic phases were found in the samples doped with Co 2+ , Cu 2+ and Zn 2+ ions; however, we found that incorporating Zn 2+ into calcium hydroxyapatite stabilizes only the monoclinic phase.

Hydrothermal-assisted sol–gel synthesis of Cd-doped TiO2 nanophotocatalyst for removal of acid orange from wastewater

This research is based on synthesis of titania (TiO2) nanophotocatalyst followed by cadmium (Cd) doping to activate the photocatalyst in visible part of the light spectrum. Therefore, the Cd–TiO2 nanophotocatalyst was synthesized in various Cd/Ti molar ratios of 0, 0.05, 0.1, and 0.15 using hydrothermal-assisted sol–gel method. The characterization analyses of X-ray diffraction, field emission scanning electron microscopy, brunauer-emmett-teller, diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric-derivative thermogravimetric, transmission electron microscopy, and energy dispersive X-ray were carried out to evaluate the physical, chemical, and optical properties of the catalysts. The X-ray diffraction analysis resulted a decrease in the crystallinity due to cadmium doping. Field emission scanning electron microscopy images have confirmed the nano-sized structure of the catalysts. The analysis also has demonstrated particle size distribution enhancement with a meaningful low average particle size for Cd/TiO2 (0.15) sample. This sample has represented the highest brunauer-emmett-teller surface area. According to energy dispersive X-ray dot mapping analysis, no aggregation was detected on the catalyst surface. Diffuse reflectance spectroscopy analysis has indicated a moderate decrease in band gap, after Cd loading. The photocatalytic degradation of acid orange 7 dye from the synthetic wastewater was carried out to evaluate the photocatalytic activity. The most effective parameters on the process, such as pH, catalyst loading, and dye concentration, were investigated. According to the characterization analyses and degradation tests, Cd/TiO2 (0.15) was selected as a sample having best structural properties and photocatalytic activity. Finally, the experiments resulted the optimum conditions of pH = 2, catalyst loading of 1 g/L, and dye concentration of 10 mg/L, indicating 95 % of dye degradation after 120 min of experiment. The electron–hole pair generation via transition of electron between the valence and conduction bands (band gap) is the fundamental of any photocatalytic process. After Cd doping, the conduction band position shifts toward the valence band. Then, a valence electron in narrow band gap photocatalyst needs lower energy of light to transfer to conduction band, it means that using light in higher wavelengths (visible light spectra) will be available. In photocatalytic wastewater treatment process, degradation occurs in two ways: the first mechanism is direct oxidation-reduction through electron–hole generation, and the second one would be the oxidation through produced reactive species such as hydroxyl radicals, this route of reaction organizes the major part of wastewater treatment.