Synthesis and Empirical Analysis of the Thermophysical Characteristics of GO-Ag Aqueous Hybrid Nanofluid Using Environmentally Friendly Reducing and Stabilizing Agents

Te remarkable potential of the carbon allotrope graphene and its derivatives in developing hybrid nanofuids has sparked considerable interest among researchers. Tese carbon nanoparticles ofer excellent opportunities to blend with various metal or metal oxide nanoparticle binders to improve their material properties. Tis study focuses on investigating the synthesis, characterization


Introduction
Te use of graphene-based nanoparticles in both solid metal structures and liquids has created opportunities for various applications such as thermal power generation, clean and renewable energy, heat transfer, electronic cooling, and bioenergy.Tis is because graphene nanoparticles have better chemical, mechanical, electrical, and thermophysical properties [1][2][3][4][5].However, there are some challenges associated with graphene nanoparticles, such as difculties in bulk production and their hydrophobic nature, which leads to low stability with water.Tese issues led to the development of graphene oxide (GO) as one of the alternatives to graphene.Tese GO nanoparticles are simple to prepare on a large scale, are cost-efective, have high thermal conductivity, and are hydrophilic towards water molecules, making them an ideal candidate for thermal investigations [1,6].To this end, Hajjar et al. [7] studied the thermal conductivity of fve diferent concentrated GO nanofuids (0.05 wt.%-0.25 wt.%) at operating temperatures ranging from 10 °C to 40 °C.Te authors found that at 40 °C and 0.25 wt.%, there was a maximum increase in thermal conductivity of 47.54%.
Te authors also noted that the thermal conductivity of the GO nanofuid increased with temperature and nanoparticle concentration.In a similar vein, the research conducted by Mei et al. [8] delved into the thermal and rheological characteristics of GO nanofuids with low mass fractions ranging from 0.002% to 0.01% at temperatures between 25 °C and 50 °C.Te authors discovered that at 0.01% and 50 °C, the GO nanofuid displayed higher thermal conductivity than other low concentrations.Te authors' observations mirrored those of Hajjar et al., and they further reported that an increase in temperature and nanoparticle concentration led to a decrease and increase in nanofuid viscosity, respectively.Te literature discussed above indicates that GO nanofuids can substantially enhance the thermal conductivity of base fuids even at low concentrations.GO nanostructures possess multiple characteristics, including a higher surface-to-volume ratio, high charge carrier mobility, high thermal conductivity, tunable porosity and band gap, good catalytic properties as electron acceptors, high elasticity, longer stability duration, and many more, depending on the application requirements [9].Tese multiple combinational characteristics make GO nanoparticles suitable for use as mono or hybrid nanoparticles.Several researchers have used GO nanoparticles as a core material and doped them with metal and metal oxide nanoparticles [10][11][12][13][14] to produce novel hybrid nanoparticles or nanofuids.Te thermophysical, optical, chemical, and biological properties of the doped nanoparticles were enhanced through this process.For instance, Li et al. [15] prepared an ethylene glycol-based GO-Ag hybrid nanofuid and observed an increase in thermal conductivity of 22% at 45 °C with a mass fraction of 0.3 wt.% in the temperature and mass fraction range of 20-45 °C and 0.1, 0.2, and 0.3 wt.%, respectively.Later, the researcher Huminic et al. [16] conducted research on a GO-Si aqueous hybrid nanofuid and reported empirical and numerical fndings on the nanofuid's viscosity impact at temperatures ranging from 20-50 °C.Tey provided a detailed report indicating that the nanofuid's thermal performance would improve due to the reduction in viscosity at higher temperatures.Singh et al. [17] found a 30% improvement in the thermal conductivity of GO-CuO/DW nanofuids at 0.3 wt.% and 60 °C.Taherialekouhi et al. [18] discussed the preparation of aqueous GO-Al 2 O 3 hybrid nanofuid at 0.1, 0.25, 0.5, 0.75, and 1% volume fractions from 25-50 °C and found 33.9% improvement in the thermal conductivity at 1% and 50 °C.Te authors also performed mathematical modelling for the experimental thermal conductivity ratio results, infuencing the volume fraction and change in temperature of the hybrid nanofuid.El-Shafai et al. [19] investigated the thermal characteristics and ability of ternary GO@CuO/Al 2 O 3 hybrid nanofuids in solar applications.Te researchers observed a 22.56% improvement in thermal conductivity compared to the aqueous base fuid at 0.2 wt.% and 50 °C.As a result, much research has been conducted on using GO as a core material for doping with metal oxides rather than metal nanoparticles and at higher concentrations instead of low concentrations.
Tis study focuses on the synthesis, characterization, and investigation of the stability and thermophysical characteristics of hybrid nanofuids containing Ag-decorated GO nanoparticles.Te nanofuid is prepared with nanoparticle dispersions of less than 0.5 wt.% and at various weight percentages (0.025 wt.%, 0.05 wt.%, 0.1 wt.%) in doubled distilled water (DW).Furthermore, the response surface methodology (RSM) is employed to analyse the experimental thermal conductivity results.Te RSM approach is crucial for performing precise regression analysis to forecast the mathematical model using experimental data.Previous studies have used RSM multivariate regression to evaluate the thermal characteristics of diferent nanofuids associated with input data such as temperatures and weight volume concentrations [20][21][22].

Materials and Procedures
2.1.Graphene Oxide (GO) Nanoparticles Fabrication.In this research, all chemicals purchased were of analytical grade and sourced from Sigma Aldrich, USA; Otto Chemie Private Ltd; Avra Synthesis Private Ltd; and Sisco Research Laboratories Pvt Ltd, India.Te graphene oxide nanoparticles were synthesized using Hummer's modifed approach [12,23].Initially, 3 grams of natural graphite fakes were combined with 3 grams of NaNO 3 in a purifed 500 mL round-bottom fask.Ten, 90 mL of concentrated H 2 SO 4 was added with vigorous agitation at 0-5 °C.After 3 to 4 hours, 12 g of solid KMnO 4 was slowly added in parts at temperatures below 15 °C in an ice bath attributable to an exothermic reaction.Te addition of chemicals was done at a slow pace.After 2 hours, 184 ml of distilled water was incorporated, and the compound was continuously stirred at room temperature for about two hours.Te slurry was then refuxed at 98 °C for 15 minutes, cooled to room temperature (RT), and agitated for two hours.Te solution turned bright yellow after gently infusing 40 ml of H 2 O 2 and was swirled for an hour with 400 ml of distilled water.Te upper layer of water was subsequently extracted, followed by the addition of 10% HCl.Te mixture was then subjected to centrifugation, and this process was repeated multiple times.Te GO nanoparticles were washed with DW until the pH approached neutral, culminating in a gel-like material.Te nanoparticles were dried at 60 °C in a vacuum hot air oven and preserved in the dark.

GO-Ag Hybrid Nanoparticles Synthesis
. Figure 1 presents a graphical representation of the synthesis process and molecular structure of GO-Ag hybrid nanoparticles.Te GO-Ag nano-hybrids were prepared using presynthesized GO nano powder and Ag metal precursor derived from silver nitrate (AgNO 3 ), following established procedures [12,24].Silver nanoparticles (AgNPs) were obtained by reducing AgNO 3 in an aqueous solution with ascorbic acid as the reducing agent and trisodium citrate as the stabilizing agent to control the size and shape of the silver nanoparticles [25].Te typical process involved sonicating 1 g of GO in 100 ml of the aqueous solution for 2 hours.Subsequently, 2 Advances in Materials Science and Engineering 6 × 10 −2 M AgNO 3 dissolved in 100 ml of the aqueous solution, along with an aqueous trisodium citrate solution (1 ml, 10 −3 M) and freshly prepared ascorbic acid (1 ml, 10 −3 M), was gradually added to the AgNO 3 solution while continuously mixing for 1 hour at room temperature (RT).Te resulting solution containing silver nanoparticles was added dropwise to the GO nano-solution while stirring at a constant speed of 90 rpm using a magnetic stirrer.Te mixture was then left undisturbed for 48 hours at room temperature in the absence of light and without heating, resulting in the formation of GO-Ag-doped solutions.Te GO-Ag solutions underwent centrifugation and were rinsed with DW and ethanol fve times.Finally, they were cured at 50 °C in a vacuum hot air oven to produce Ag-decorated hybrid nanoparticles.

GO-Ag Nanofuid Synthesis.
A two-step approach was utilized to prepare the GO-Ag hybrid nanofuids from doubled distilled water and the synthesized hybrid nanoparticles of GO-Ag.After fxing the mass of the base fuid (m bf ) and the weight percentage of nanoparticles (φ), the mass of the synthesized hybrid nanoparticles was estimated using the following equation: Te mass (m np ) of the synthesized GO-Ag nanohybrids was measured utilizing a high-precision digital balance (0.001 g).To obtain the various weight percentages (0.025%, 0.05%, and 0.1%) of the hybrid nanofuids, the respective known masses of the hybrid nanoparticles and the base fuid were mixed in an ultrasonic device for 30 minutes.Subsequently, constant stirring was carried out in a magnetic stirrer for one hour to achieve better dispersion of the hybrid nanofuids.

Measurement of Termophysical Properties.
A viscometer (LVDVE, Brookfeld Engineering Labs, USA) was used to test the viscosities of the nanofuids, which has a precision of ±1%.A KD2 Pro thermal property analyzer (Decagon Devices Inc., USA) employs a KS-1 sensor in a measurement range of 0.02-2 W/m.K and a precision of ±5%.

Findings and Critical Analysis
3.1.Findings of XRD.Te X-ray difraction pattern of the Ag deposition on the GO nanosheet is depicted in Figure 2, using the copper anode (k α1 � 1.54060).Te difractograms display steep peaks and broad patterns, indicating the presence of crystalline elements.Te percentages of crystalline and amorphous phases confrm the deposition of Ag over GO at 36.95% and 63.05%, respectively.Te difracted peaks at Braggs angle 2θ � 11.1 °and 16.94 °confrm the presence of GO, while the peaks of Ag were observed at scattering angles of 38.1 °, 44.3 °, 64.5 °, and 77.3 °with h k l plane indices of (111), ( 200), (220), and (311).Tese peaks matched the space group Fm-3m with JCPDS Card no.07-0783 [24], indicating the successful synthesis of the Ag-decorated GO hybrid nanoparticle.

Findings of FTIR.
Te investigation of the associations among all synthesized elements was conducted using the FTIR spectrum analysis.Te transmittance proportion and wavenumbers of GO and GO-Ag hybrid nanoparticles were compared.Figure 3 shows that the broad spectral band at 3380.2 cm −1 and 1060.78cm −1 corresponds to the O-H bending vibration of carboxylic acid and phenolic acid structural units, which indicates the presence of GO nanosheet [12].Te wavenumber 2360.71cm −1 indicates the C-O bond, representing the bonding of crystalline elements.

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Te functional bands at 1729.6 cm −1 and 1615.27cm −1 are attributed to the asymmetric and symmetric carbonyl stretch vibrations of COOH groups (C�O), respectively.In the GO-Ag spectral bands, the peaks of the GO spectrum were reduced due to the doping of Ag nanoparticles over the GO layer.
Te contact between the silver nanoparticles and the GO nanosheets' functional groups encompassing oxygen was stable by reversing the asymmetric and symmetric stretching processes.Tat is, the depth of the asymmetric −(COO) elongation diminished, while the intensity of the symmetric −(COO) elongation escalated [24].4 Advances in Materials Science and Engineering

Particle Size Analyzer.
In order to determine the mean size diameter of the fabricated GO-Ag hybrid nanoparticle observed in Figure 4, the dynamic light scattering (DLS) method was applied.Te DLS fndings revealed that the synthesized nanocomposite has a mean particle size of 44 nm in precision and a particle size distribution of 30-80 nm.
3.4.Scanning Electron Microscope. Figure 5(a) illustrates the successful synthesis of an amorphous, worm-like structure of graphene oxide nanoparticles, forming silky wrinkled veils [26].Te image also highlights that the single-layer thickness of the GO nanosheet is greater than that of graphene due to the presence of covalently linked oxygen and displaced sp 3 hybridized carbon atoms, situated above and below the original graphene plane [7].A small section of the image was analysed using ImageJ to determine the surface roughness of the GO nanoparticle, and the results confrmed that the GO nanosheet's surface was smooth, indicating that the formulation procedures and functional units were linked to the chemical process.On the other hand, the evenly distributed quasi-cubical Ag nanoparticles on the GO nano silk veil were found to have a rougher surface than the GO nanosheet (analysed in Image J), which confrms the frm decoration of Ag nanoparticles on the GO, as observed in

EDS Analysis. Te chemical composition analysis of GO-Ag hybrid nanofuids was conducted utilizing Energy
Dispersive Spectroscopy (EDS), revealing weight percentages of carbon (C)-30.4%,oxygen (O)-39.8%,and silver (Ag)-29.8%,as summarized in Table 1.Te presence of carbon, oxygen, and silver confrms the existence of graphene oxide and silver nanoparticles, respectively, in its combined form.Te elemental mappings depicted in Figure 6 illustrate the high purity and uniform distribution of Ag nanoparticles anchored over the GO nanosheets.Te EDS analysis demonstrates the transmission of carbon and oxygen electrons from the K shell and Ag from the M shell due to their high ionization energies.

UV Vis Analysis.
Te UV spectral analysis results, depicted in Figure 7, confrm the successful formation of GO-Ag nanohybrids and are compared to the absorption band of GO nanoparticles.Te nanofuids showed a pronounced absorption peak at wavelengths of 234 nm (GO) and 256 nm (GO-Ag), indicating the presence of GO nanoparticles [12].Te broad adsorption spectra at 400 nm (GO-Ag) correspond to the formation of Ag nanoparticles, which are not present in the GO spectrum.Tis is mainly due to the refection of the Ag nanoparticle impinging on the surface of the GO nanosheet [12].Tis Ag impingement results in a change in the formation of sp 2 polyaromatic carbon, causing a shift in the wavelength from 234 to 256 nm, signifying the partial reduction of GO during the synthesis of the GO-Ag nanohybrids.Moreover, it is associated with a signifcant reduction in the OH group spectral bands and changes in the asymmetrical and symmetrical spectral bands of GO-Ag, as revealed in the FTIR spectrum.

Termal Conductivity.
Tis section presents an investigation into the thermal conductivity of DW (0 wt.%) and GO-Ag hybrid nanofuid with diferent weight percentages (0.025 wt.%, 0.05 wt.%, 0.1 wt.%).Prior to evaluating the thermal conductivity (K) of the hybrid nanofuids, the K value of DW was measured and assessed using standard data (Incorpera, Dewitt, Bergman, and Lavine) [27], as depicted in Figure 8, which shows a good agreement between the measured and standard parameters.
Te precise data was acquired by maintaining the GO-Ag nanofuid samples and the device in a constant-temperature bath for approximately ffteen minutes to achieve equilibrium.Te mean of the observed values, with a correlation coefcient exceeding 0.99, was used to determine the sample's K value at a specifc weight percentage.
Te results indicate that the prepared hybrid nanofuids have a notable improvement in thermal conductivity with a temperature rise from 293 K to 333 K, as shown in Figure 9. Tis increase is primarily due to the Brownian motion of the dispersed GO-Ag nanoparticles in the base fuid, as the collision of the hybrid nanoparticles leads to the transfer of kinetic energy into thermal energy, resulting in the transfer of energy from the nanoparticles to the water molecules and an increase in the K value of the hybrid nanofuids.
Among the diferent concentrations and base fuids, the 0.1 wt.% hybrid nanofuid showed the most optimal results at both lower and higher temperatures.For example, at the temperature range of 293 K to 333 K, the thermal conductivity enhancement was about 6.69% to 15.29%, 11.04% to 22.63%, and 15.22% to 31.19% for 0.025 wt.%, 0.05 wt.%, and 0.1 wt.%, respectively, than the base fuid.Tis demonstrates that the K values increase linearly with temperature.
Te thermal conductivity ratio (K nf /K bf ) of GO-Ag was observed to be greater than one, signifying its superior performance and efciency as a heat transfer fuid (Figure 10).Specifcally, it was determined that the K nf /K bf increased within the ranges of 1.06-1.15,1.11-1.22,and 1.15-1.31for concentrations of 0.025 wt.%, 0.05 wt.%, and 0.1 wt.% over a temperature range of 293 K to 333 K, respectively, in comparison to the base fuid.
3.8.Viscosity.Viscosity (µ) plays a crucial role in infuencing the heat fow in nanofuids.Te increase in nanoparticle concentration in base fuids causes an increase in viscosity, which ultimately afects the heat transport capabilities.In this study, the viscosity of hybrid nanoparticles with three diferent weight percentages (0.025%, 0.05%, and 0.1%) was investigated using a Brookfeld digital viscometer (LVDV-E, Brookfeld, USA).
Te viscosity of each sample was determined using spindle S61, which is specifcally designed for low-viscosity fuids, while maintaining a consistent shear rate and spindle speed of 30 rpm.Te viscosity of each sample was measured in fve replicates.

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Te results shown in Figure 11 indicate that the viscosity of hybrid nanofuid decreases with increasing temperature.Te viscosity of GO-Ag hybrid nanofuids does not vary signifcantly from that of the base fuid, and the diference in viscosity between GO-Ag nanofuids and the base fuid decreases as the temperature increases.At 293 K, the viscosity of 0.1 wt.% was higher than that of other nanofuid concentrations.However, as the temperature increased, the viscosity of 0.1 wt.% approached that of the base fuid viscosity.Te fndings suggest that the µ values increase exponentially with an increasing proportion of GO-Ag nanoparticles.However, as the temperature rises with higher concentrations of nanoparticles, viscosity decreases at

Comparison between Experimental Results of (K nf /K bf )
and Standard Correlated Models.In order to relate the experimental results (K nf /K bf ) to the appropriate correlated standard models, some well-known prominent thermal conductivity models from the past and present were used in this study.Like the Maxwell model [28] in (2), it is the most popular, conventional, and used by many researchers to correlate their experimental fndings, where K nf is the thermal conductivity of the nanofuid, K bf is the thermal conductivity of the base fuid, and K p is the nanoparticle thermal conductivity coefcient.

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Later, Lu and Lin [30], in equation ( 4), similar to Timofeeva et al., postulated a relationship based on nanoparticle concentration.
While experimenting with the thermophysical characteristics of graphene oxide and alumina nanoparticles, Taherialekouhi et al. [18], in equation ( 5), suggested a model between both the concentration and temperature of nanoparticles as dependent elements.
Te empirical thermal conductivity ratio of the GO-Ag nanofuid was compared to various standard models, and the results were presented in Figures 12(a)-12(e).It was observed that the empirical K nf /K bf of the nanofuid performed signifcantly better than the standard models.For instance, at 333 K, the experimental K nf /K bf of GO-Ag showed a remarkable increase of 12.67% compared to the Taherialekouhi et al. model.Hence, the empirical K-ratio results were found to deviate from the standard relations mentioned earlier.However, to investigate the thermal conductivity of GO-Ag nanofuid, a suitable mathematical model was proposed using the response surface methodology (RSM) approach.We meticulously analysed the experimental thermal conductivity ratio and precisely predicted a mathematical model that fts the experimental data.

RSM Regression Model.
Te Response Surface Methodology (RSM) approach was employed to establish a linear correlation in this study.Response surface regression analysis is a well-known technique in design of experiments (DOE) applications [20,31].Te input data was examined with respect to the experimentally measured results to determine the fnal output.Te primary objective was to create a statistical and mathematical model based on empirical K ratio values of GO-Ag nanofuid.Te accuracy and reliability of the created regression model were evaluated using the analysis of variance (ANOVA) approach, as presented in Table 2.A correlation between the predicted and experimental results can only be achieved when the R 2 value is close to one.In this study, the regression analysis of the experimental results produced an R 2 value of 0.99, indicating a better correlation between predicted and empirical values.Te quadratic regression analysis was preferred over other analyses such as 2FI, linear, and cubic, as it resulted in a very low p value of 0.0001 and a higher Fisher test value (F-value).Te p value should be less than 0.05 to achieve better optimization [20].Te predicted equation for the K  Advances in Materials Science and Engineering ratio of the GO-Ag nanofuid is provided by equation ( 6), with temperature (T in K) and weight percentage (φ) as constraint factors at low and higher concentrations (0.025 wt.% < φ < 0.1 wt.%) of GO-Ag hybrid nanofuids.
Te nanoparticle concentration factor (φ) in the proposed model was found to be the most signifcant and preferable factor compared to temperature based on the variance analysis results.
Te regression model proposed using RSM analysis accurately fts the experimental data, with most of the predicted points being close to the experimental values shown in Figures 12(a)-12(e).
Te contour and three-dimensional diagrams of the proposed model are presented in Figure 12(f ).It was observed that the K nf /K bf improved with an increase in both T and φ of nanoparticles. Figure 13 compares the empirical and predicted results of K nf /K bf , showing the maximum percentage deviation between and predicted to be ±1.2%.Tis deviation indicates an acceptable mathematical correlation with the experimental results.Table 3 shows the comparison between the results of the actual and predicted thermal conductivity ratios of GO-Ag hybrid nanofuids with residual errors, leverage, and externally studentized residuals.

Processes Governing Thermal Conductivity Augmentation in GO-Ag Nanofluid
Te impact of several key processes enhanced the K value of GO-Ag hybrid nanofuids.Following are a few contributing factors that impact the improvement of thermal conductivity.
(1) Brownian motion [15,32]: As the temperature of the hybrid nanofuids increased, the dispersed GO-Ag hybrid nanoparticles began to move randomly due to the excess heat.Tis resulted in relative lateral motion and collisions between the particles, converting kinetic energy to thermal energy and dissipating it to the base fuid's molecules.Tis prolonged contact between particles and molecules promoted microconvectional heat transport, enhancing nanoscale conduction and convection heat transfer.(2) Clustering of nanoparticles [33,34]: Te surface area of GO and Ag nanoparticles is increased due to clustering, as observed in SEM images of Ag nanoparticles clustered on the surface of GO nanosheets.Tese clusters improve interaction with the fuid layers, enhancing microconvective heat transfer and thermal conductivity.Te liquid layers adjacent to the enhanced surface behave like solid surfaces at the solid-liquid interface, improving heat transfer from the nanoparticle to its next liquid layer.(3) Electron-phonon collision: A relatively high thermal conductivity performance factor was observed at higher temperatures, possibly due to the aforementioned factors.Electron-hole pair excitation and electron-electron collisions may occur in dispersed hybrid nanoparticles due to thermal efects.Te presence of external energy results in electron lattice collisions, coupling low-level energy electrons to phonons, and increasing the temperature of metal lattices.Heat produced in the metal lattice dissipates into the surrounding fuid molecules through phonon-phonon scattering [35].Tis phenomenon causes the heat to dissipate from the energized nanoparticles into the base fuid, contributing to the increase in thermal conductivity.(4) Other factors, including surface chemical efects, atomic force, crystalline nature, and nanoscale rotation of nanoparticles due to temperature increase, also contribute to the development of the K value of the hybrid system.
Te electrokinetic potential (zeta potential) value was measured to indicate the repulsive force and stability of the nanoparticles in the base fuid.Te greater the values of the zeta potential (either positive or negative), the greater the stability of the nanofuids.
Nanofuids with a value greater than ±30 mV were considered to possess higher repulsive forces between particle suspensions, resulting in less agglomeration and good stability [34].Te zeta potential result of the GO-Ag hybrid nanofuid sample, as shown in Figure 14, had a mean value of −35.6 mV, indicating that the nanofuid was highly stable with a considerable negative repellent potential.
Furthermore, the UV absorbance of the silver nanoparticles at λ � 400 nm in GO-Ag hybrid nanofuids was analysed in Figure 15.Te observed results showed hardly any changes in wavelength or absorbance value after 25 days of measurements in the UV-visible spectrometer, demonstrating the high stability of the hybrid nanofuids.Tis stability might be due to the functional group on the interface of the GO nanoparticles, which anchored the strong bond with the Ag nanoparticles, and the infuence of reducing and stabilizing agents on the Ag nanosurface decreased the agglomeration of nanoparticles to settle down and in reaction with water molecules.Terefore, it is presumed that the prepared hybrid nanofuids are stable in all applications.Advances in Materials Science and Engineering

Conclusion
Te low-cost chemical reduction technique was utilized to synthesize the GO-Ag hybrid nanoparticles.A detailed experimental investigation was conducted on the preparation, characterization, and thermophysical properties of the GO-Ag hybrid nanofuids at diferent weight percentages.Te following fndings were established: (1) Te particle size analyzer, XRD, FTIR, UV, SEM, and EDX analyses demonstrated that the hybrid structure comprised signifcant molecular linkages of all elements (GO and Ag).(2) Te K and µ values of the hybrid nanofuids were found to be in agreement and increased with increasing concentrations of the nanoparticles.(3) At 333 K temperature in 0.1 wt.%, the GO-Ag nanofuid exhibited the highest thermal conductivity enhancement of 31.19% compared to the base fuid.(4) Te K ratio of GO-Ag hybrid nanofuids was evaluated by comparing it to standard models.A mathematical relationship was derived using RSM methodology based on the empirical values of the thermal conductivity of GO-Ag hybrid nanofuids as a function of temperature and weight percentage.Compared to other standard equations discussed, the derived equation showed a better correlation with the empirical results.(5) Zeta potential and UV visible spectrum analyses confrmed the stability of the nanofuids.Due to their improved thermophysical properties, GO-Ag nanofuids could be an excellent choice for heat transport fuids in applications such as solarthermal and heat exchanging equipment.

Figure 1 :
Figure 1: Graphical depiction of the process and molecular structure of GO-Ag hybrid nanoparticles.

Figure 2 :Figure 3 :
Figure 2: X-Ray difractogram pattern of GO and GO-Ag hybrid nanoparticles.

Figure 6 :Figure 7 :Figure 8 :
Figure 6: EDS analysis of GO-Ag nanoparticles and elemental mapping of SEM image, C, O, and Ag.

Figure 12 :
Figure 12: (a-e) Comparison of weight percentage of nanofuids vs thermal conductivity ratio at diferent temperatures ranging from 293 K-333 K, and (f ) contour and three-dimensional diagram of the proposed correlation.

Figure 14 :
Figure 14: Zeta potential analysis and pictorial view of prepared samples.

Table 2 :
ANOVA-type III-partial sum of squares.

Table 3 :
Comparison of actual and predicted thermal conductivity ratios.Wt.(%) Temperature (K) Actual K-ratio Predicted K-ratio