Aggregation Of Graphene Oxide Research Articles

Defoaming and Toughening Effects of Highly Dispersed Graphene Oxide Modified by Amphoteric Polycarboxylate Superplasticizer on Oil Well Cement

The aggregation of graphene oxide (GO) during the hydration process limits its wide application. Polymer superplasticizers have been used to improve the dispersion state of GO due to their adsorption and site-blocking effects, though the formation of a large amount of foam during the mixing process weakens the mechanical properties of cement. A highly dispersed amphoteric polycarboxylate superplasticizer-stabilized graphene oxide (APC/GO) toughening agent was prepared by electrostatic self-assembly. Results demonstrate that the APC/GO composite dispersed well in a cement pore solution due to the steric effect offered by the APC. Additionally, the well-dispersed GO acted as an antifoaming agent in the cement since GO nanosheets can be absorbed at the air–liquid interface of APC foam via electrostatic interactions and eliminate the air-entraining effect. The well-dispersed APC/GO sheets promoted cement hydration and further refined its pore structure owing to the nucleation effect. The flexural and compressive strength of the cement containing the APC/GO composite were enhanced by 21.51% and 18.58%, respectively, after a 7-day hydration process compared with a blank sample. The improved hydration degree, highly polymerized C-S-H gel, and refined pore structure provided enhanced mechanical properties.

The dispersion and influence of graphene-oxide-modified polycarboxylate superplasticiser in alkaline cement solution

The aggregation of graphene oxide (GO) in alkaline solutions is a critical factor that limits its potential applications in cement-based materials. In this study, a polycarboxylate superplasticiser (PCE) was employed as a dispersant and a GO–PCE water-reducing agent was synthesised through the method of dropwise addition. This synthesis approach not only preserved the water-reducing capabilities of PCE but also enhanced the dispersibility of GO in alkaline cement solutions. Furthermore, the synthesis method is straightforward. The results showed that that GO–PCE had excellent dispersion in a saturated calcium hydroxide (CH) solution. Furthermore, it was found that the GO–PCE enhanced the workability of cement, accelerated cement hydration, reduced the crystallite size of the CH and increased the compressive strength of the cement mortar.

Principles determining the aggregation of graphene oxide in aqueous solutions: The effect of heterogeneous distribution of oxygen-containing groups

Molecular dynamics (MD) simulations were conducted to investigate the effects of heterogeneous distribution of oxygen-containing groups on the aggregation modes of graphene oxide (GO) flakes in aqueous solution. The results show that the aggregation of GO flakes can be divided into Brownian motion, adsorption, and adjustment steps, where the adsorption step further can be classified as point-falling-line-squeezing-plane (PFLSP) mode and bridge adsorption of confined water molecules mode. When the aggregation happens at the non-oxidized region, the successful aggregation is always accompanied by the PFLSP mode. In contrast, at the oxidized region, the bridge adsorption of CWMs mode is preferred.

Aggregation of graphene oxide upon the stripping of oxidized debris: An experimental and molecular dynamics simulation study

The most recent structural study of graphene oxide (GO) indicates that the oxidized debris (ODs) adhered to as-prepared GO will strip in certain aquatic settings. The impact of ODs stripping on the characteristics of GO has been widely reported, but its effects on GO aggregation have received less attention. Here, the influence of OD stripping on the GO aggregation property was identified, and the aggregation of as-prepared GO and GO upon OD stripping was compared. Upon ODs stripping, the pKa values of GO shifted from 3.91, 6.25, and 9.84 to 4.54, 6.65, and 10.21, respectively. Further analysis indicated the removal of ODs reduced the net negative charge and improved the hydrophobicity of GO, hence promoting the aggregation of GO. The acceleration of GO-Ca2+-OD aggregate formation was facilitated by the collective effects of ODs stripping, functional group deprotonation, double layer compression, OD bridging, and charge neutralization. The metal ions and stripped ODs attach to GO edges and link GO, which perform like bridges and contribute to further aggregation. In general, the existence of ODs adds complexity to the constructions and characteristics of GO, and it is important to take this into account while evaluating the aggregation characteristic of GO-based materials.

Fabrication and structural modification of graphene oxide-tetraethyl orthosilicate solution via liquid-phase pulsed laser ablation

Liquid-phase pulsed laser ablation (LP-PLA) is a physical deposition technique to fabricate micro- and nanoscale particles of polymer, glass, and ceramic materials. In this work, graphene oxide (GO) that was immersed in tetraethyl orthosilicate (TEOS) and ethanol was used to fabricate the graphene-silicone polymer using the LP-PLA technique. The GO-TEOS solution was ablated with different fluences of the laser. The ablated GO-TEOS solution was characterized by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive x-ray, and ultraviolet-visible (UV-Vis) spectroscopy to study the graphene-silicone polymer properties. The FTIR result shows that the laser ablation has provided sufficient laser energy to create or break the chemical species of GO and TEOS compounds as observed on Si–O and C–O bonds. The Raman result shows the changes in the intensity in the D band, which suggests that the carbon atom of the GO has been functionalized with other compounds. Several large flakes were observed in the SEM images, representing the silicon polymer with the GO aggregation. The particle size in the range of 3–8 and 66–110 μm was formed due to the presence of uniformly sized nanoparticles of the GO-TEOS mixture and aggregation of the GO-TEOS nanoparticles into clusters. The zeta potential results indicated that the stability of the GO-TEOS mixture decreases after laser ablation. The UV-Vis result shows a broad absorption band with center at 492 and 532 nm with increasing absorbance at low fluence then saturated and decreased at maximum laser fluence. From the results above, several chemical interactions between GO and TEOS were observed, and the data suggested the laser fluence as the major source to cause both photothermal and photochemical reactions on the samples. In short, laser ablations provide sufficient energy to induce chemical bonding, which further allows structural modification of materials.

Application of Nanohybrid Substrates with Layer-by-Layer Self-Assembling Properties to High-Sensitivity Surface-Enhanced Raman Scattering Detection.

The present study was conducted to prepare and investigate large-area, high-sensitivity surface-enhanced Raman scattering (SERS) substrates. Organic/inorganic nanohybrid dispersants consisting of an amphiphilic triblock copolymer (hereafter referred to simply as "copolymer") and graphene oxide (GO) were used to stabilize the growth and size of gold nanoparticles (AuNPs). Ion-dipole forces were present between the AuNPs and copolymer dispersants, while the hydrogen bonds between GO and the copolymer prevented the aggregation of GO, thereby stabilizing the AuNP/GO nanohybrids. Transmission electron microscopy (TEM) revealed that the AuNPs had particle sizes of 25-35 nm and a relatively uniform size distribution. The AuNP/GO nanohybrids were deposited onto the glass substrate by using the solution drop-casting method and employed for SERS detection. The self-assembling properties of two-dimensional sheet-like GO led to a regular lamellar arrangement of AuNP/GO nanohybrids, which could be used for the preparation of large-area SERS substrates. Following removal of the copolymer by annealing at 300 °C for 2 h, measurements were obtained under scanning electron microscopy. The results confirmed that 2D GO nanosheets were capable of stabilizing AuNPs, with the final size reaching approximately 40 nm. These AuNPs were adsorbed on both sides of the GO nanosheets. Because the GO nanosheets were merely 5 nm-thick, a good three-dimensional hot-junction effect was generated along the z-axis of the AuNPs. Lastly, the prepared material was used for the SERS detection of rhodamine 6G (R6G), a commonly used highly fluorescent dye. An enhancement factor (EF) of up to 3.5 × 106 was achieved, and the limit of detection was approximately 10-10 M. Detection limits of 10-10 M and < 10-10 M were also observed with the detection of Direct Blue 200 and the biological molecule adenine. It is therefore evident that AuNP/copolymer/GO nanohybrids are large-area flexible SERS substrates that hold great potential in environmental monitoring and biological system detection applications.

Falling-Leaves Stacking Aggregation of Two-Dimensional Macromolecular Graphene Oxide in Solution.

Understanding the dynamical behaviors of two-dimensional (2D) macromolecules is of fundamental importance for the precise modulation of their assembled structures and material performances. However, considerably less is known about how discrete macromolecular sheets aggregate into extended macroscopic assemblies in solutions. The absence of a quantitative description of the assembly process limits the precise structural control of assemblies. Here, we investigated the aggregation thermodynamic transition and kinetic behavior of 2D macromolecules in the model of single layer graphene oxide (GO). Combining Flory-Huggins theory with experimental observations, we unveiled the critical thermodynamic transition of GO to correlate with the solvent property. We proposed a theoretical falling-leaf model to quantitatively describe the kinetic aggregation process of 2D GO sheets. Experimental analysis validated the theoretical prediction that the thickness of GO aggregates has a power law relation with the poor solvent content. Our work provides a fundamental understanding of phase separation of 2D macromolecules and offers an insight into modulating the aggregated structures of their assembled materials.

Promotion effect of ultraviolet light on graphene oxide aggregation in the presence of different climatic zone's humic and fulvic acid

Aggregation of graphene oxide (GO) is significantly affected by dissolved organic matter (DOM) in natural waters, while DOM's climate zone and light irradiation is seldom considered. This study investigated the effect of humic/fulvic acid (HA/FA) from various climate zones of China on aggregation of small (200 nm) and large (500 nm) GO under 120-h UV irradiation. GO aggregation was promoted by HA/FA because UV irradiation decreased hydrophilicity of GO and steric forces among particles. GO generated electron and hole pair under UV irradiation, which reduce GO with more hydrophilic oxygen-containing functional group (C-O) to rGO with high hydrophobicity and oxidize DOM into organic matter with smaller molecular weight. Most severe GO aggregation was observed with Makou HA from Subtropical Monsoon climate zone and Maqin FA from Plateau and Mountain climate zone, which was primarily because HA/FA's high molecular weight and aromaticity dispersed GO initially that facilitated UV penetration. GO aggregation ratio was positively correlated with graphitic fraction content (R2 = 0.82-0.99) and negatively correlated with C-O group content (R2 = 0.61-0.98) in the presence of DOM under UV irradiation. This work highlights different dispersity of GO during photochemical reactions in various climate zones, providing new insight into the environmental implications of nanomaterial release.

In Situ Synthesis of Ni-BTC Metal-Organic Framework@Graphene Oxide Composites for High-Performance Supercapacitor Electrodes.

In response to serious ecological and environmental problems worldwide, a novel graphene oxide (GO) induction method for the in situ synthesis of GO/metal organic framework (MOF) composites (Ni-BTC@GO) for supercapacitors with excellent performance is presented in this study. For the synthesis of the composites, 1,3,5-benzenetricarboxylic acid (BTC) is used as an organic ligand due to its economic advantages. The optimum amount of GO is determined by a comprehensive analysis of morphological characteristics and electrochemical tests. 3D Ni-BTC@GO composites show a similar spatial structure to that of Ni-BTC, revealing that Ni-BTC could provide an effective framework and avoid GO aggregation. The Ni-BTC@GO composites have a more stable electrolyte-electrode interface and an improved electron transfer route than pristine GO and Ni-BTC. The synergistic effects of GO dispersion and Ni-BTC framework on electrochemical behavior are determined, where Ni-BTC@GO 2 achieves the best performance in energy storage performance. Based on the results, the maximum specific capacitance is 1199 F/g at 1 A/g. Ni-BTC@GO 2 has an excellent cycling stability of 84.47% after 5000 cycles at 10 A/g. Moreover, the assembled asymmetric capacitor exhibits an energy density of 40.89 Wh/kg at 800 W/kg, and it still remains at 24.44 Wh/kg at 7998 W/kg. This material is expected to contribute to the design of excellent GO-based supercapacitor electrodes.

In Situ Fabrication of High Dielectric Constant Composite Films with Good Mechanical and Thermal Properties by Controlled Reduction

As a common two-dimensional carbon material, graphene has been widely doped into polymers to prepare high-performance dielectric materials. However, the shortcomings of graphene, such as large specific surface area and poor dispersion, limit its further application. Therefore, in this work, to solve the problem regarding the uniform dispersion of graphene in the matrix, in situ polymerization was used to prepare graphene/polyimide films, in which 1,4-diiodobutane was used as a reduction agent to prevent the aggregation of graphene oxide (GO) during imidization. High dielectric constant composite films were obtained by adjusting the ratio of 1,4-diiodobutane in GO. The results show that the resulting graphene/polyimide composite film possessed a dielectric constant of up to 197.5, which was more than 58 times higher than that of the polyimide (PI) film. Furthermore, compared to the pure PI film, the composite films showed better thermal stability and mechanical properties. Thermal performance tests showed that the 1,4-diiodobutane added during the preparation of the composite film was thermally decomposed, and there was no residue. We believe our preparation method can be extended to other high dielectric composite films, which will facilitate their further development and application in high power density energy storage materials.

Optimisation of GraPhage13 macro-dispersibility via understanding the pH-dependent ionisation during self-assembly: towards the manufacture of graphene-based nanodevices.

GraPhage13 aerogels (GPAs) are micro-porous structures generated through the self-assembly of graphene oxide (GO) and M13 bacteriophage. As GPA fabrication involves the aggregation of GO and M13 in aqueous solution, we aim to understand its dispersibility across a wide pH range. Herein, a novel technique has been developed to relate the ionisation of functional groups to the surface charge, offering insights into the conditions required for GPA fabrication and the mechanism behind its self-assembly. The aggregation of GO and M13 was observed between pH 2-6 and exhibited dependence on the surface charge of the resulting aggregate with the M13 bacteriophage identified as the primary factor contributing to this, whilst originating from the ionisation of its functional groups. In contrast, GO exhibited a lesser impact on the surface charge due to the deprotonation of its carboxylic, enolic and phenolic functional groups at pH 6 and above, which falls outside the required pH range for aggregation. These results enhance our understanding of the GPA self-assembly mechanism, the conditions required for their fabrication and the optimal processability, laying the foundation towards its broad range of applications and the subsequent manufacture of graphene-based nanodevices.

Low Friction of Graphene Oxide Aggregates in Lubricant Oil between a Steel Ball and Glass Disk under Boundary Lubrication.

Previously, isolated nanocarbons in lubricating oils were considered essential for good lubrication. However, we observed that graphene oxide (GO) aggregates in lubricating oil have lower frictional properties than isolated dispersed GO. The GO was dispersed in polyα-olefin (PAO) using alkylamine at different ratios of GO and alkylamine, or it was heated at different temperatures to synthesize high- and low-dispersible GO-dispersed PAO. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy measurements showed that low-dispersible modified GOs retained many of the original GO chemical and structural features. Macrotribological tests between a steel ball and glass disk in GO-dispersed oil were conducted with a load of 5 N under boundary lubrication. The friction interface was observed in situ using an optical microscope. In the low-dispersible GO-dispersed PAO, many GO aggregates were observed through optical microscopy. Surprisingly, the friction coefficients decreased when the GO aggregates entered the friction interface and covered the contact area. The low-dispersible GO-dispersed PAO using alkylamine had the lowest friction coefficient of 0.05, as the GO aggregates covered the contact area. From microtribological tests with a load of 0.8 mN as well, it is assumed that the low friction of the GO aggregates originates due to the sliding between the weakest shear layers in the aligned multiple GO layers.

Silicon dioxide nanoparticles decorated on graphene oxide nanosheets and their application in poly(l-lactic acid) scaffold

IntroductionThe aggregation of graphene oxide (GO) is considered as main challenge, although GO possesses excellent mechanical properties which arouses widespread attention as reinforcement for polymers. ObjectivesIn this study, silicon dioxide (SiO2) nanoparticles were decorated onto surface of GO nanosheets through in situ growth method for promoting dispersion of GO in poly(l-lactic acid) (PLLA) bone scaffold. MethodsHydroxyl and carboxyl functional groups of GO provided sites for SiO2 nucleation, and SiO2 grew with hydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) and finally formed nanoparticles onto surface of GO with covalent bonds. Then, the GO@ SiO2 nanocomposite was blended with PLLA for the fabrication of bone scaffold by selective laser sintering (SLS). ResultThe results indicated that the obtained SiO2 were distributed relatively uniformly on surface of GO under TEOS concentration of 0.10 mol/L (GO@SiO2-10), and the covering of SiO2 on GO could increase interlayer distance of GO nanosheets from 0.799 nm to 0.894 nm, thus reducing van der Waals forces between GO nanosheets and facilitating the dispersion. Tensile and compressive strength of scaffold containing GO@SiO2 hybrids were significantly enhanced, especially for the scaffold containing GO@SiO2-10 hybrids with enhancement of 30.95 % in tensile strength and 66.33 % in compressive strength compared with the scaffold containing GO. Additionally, cell adhesion and fluorescence experiments demonstrated excellent cytocompatibility of the scaffold. ConclusionsThe good dispersion of GO@SiO2 enhances the mechanical properties and cytocompatibility of scaffold, making it a potential candidate for bone tissue engineering applications.

Efficient Adsorptive Performance of Graphene Oxide by Nano Clay

Research regarding the use of Nano clay to remove toxic GO (Graphene oxide) from wastewater was limited. Through a variety of characterization techniques and methods, the adsorption performance and mechanism of Nano clay for GO were systematically studied. The related effects of solution pH, temperature, adsorbent dose, and GO concentration were studied in detail. The results show that the aggregation and deposition of GO on Nano clay depends on the pH value of the solution and the type and concentration of the electrolyte, and the isotherm data fits well with the Langmuir equation. Under the best conditions (pH=3.0), the maximum removal rate is 97.8% (C0=60 mg·L-1), and the adsorption capacity is 245.8 mg.g-1 (C0=80 mg.L-1, T=303K, equilibrium time=24 h, m=10 mg). Specifically, the dissolution of Nano clay at a relatively low pH or a high pH value helps the aggregation of GO. The results of this study provide key information for predicting the fate of GO in the land-water transition zone where Nano clay exists.

Effect ofGOagglomeration on the mechanical properties of graphene oxide and nylon 66 composites and micromechanical analysis

AbstractNanoparticles are prone to aggregation in the matrix under the action of surface energy, chemical bonding, electrostatic attraction, and van der Waals forces. Based on the molecular dynamics method, the tensile properties of graphene oxide (GO)‐reinforced nylon 66 composites were simulated and calculated, and the stress–strain curves, atomic stress clouds, and changes in the number of hydrogen bonds were obtained for the composites under tensile loading, and the effects of GO agglomeration on the mechanical properties of GO/PA66 composites were analyzed. When the GO mass fraction accounted for 90.3%, 80.5%, and 70.6% of the model, respectively, the mechanical properties of the composites decreased by 15.4%, 4.5%, and 4.2%, respectively. Because GO agglomeration in the composites made it difficult to bond effectively between GO and PA66, the number of hydrogen bonds and the type of hydrogen bonds within the model, varied with the degree of aggregation. The changes in the number of hydrogen bonds and the type of hydrogen bonds during uniaxial stretching were simulated by molecular dynamics. The number of hydrogen bonds and the type of hydrogen bonds directly affect the mechanical properties of the composites. It can be seen from the atomic stress cloud diagram that the aggregation of GO makes the mechanical properties of GO fail to exert effectively. The main stress is on the C atoms in the outermost layer of GO, while the stress on the inner layer C atoms is relatively small. As the degree of GO agglomeration decreases, the stress on each C atom of GO lamellae tends to be uniform, which effectively brings into play the excellent mechanical properties of GO and improves the mechanical properties of the composite.

Tuning liquid aggregation of zwitterionic chitin nanocrystals by graphene oxide planar catchers via electrostatic regulation

As important structural units, biomass nanomaterials have exhibited great potentials to construct high-performance macroscopic materials for broad applications by liquid assembly. However, the liquid aggregation of nanomaterials was less investigated. Here, we demonstrate that the one-dimensional (1D) zwitterionic chitin nanocrystals (ZChNCs) can be reversibly captured and released by two-dimensional (2D) planar catchers of graphene oxide (GO) sheets. The dominant electrostatic regulation strategy by pH variation drives that there are three reversible changes for the liquid aggregation of ZChNCs and GO, which were the isolated dispersion state (pH > 7), homogeneous hybridization state (7 ≥ pH ≥ 5), and partially stacked hybridization state (pH < 5), respectively. We found there are no sedimentation during the change of liquid aggregation with the higher absolute Zeta potentials (almost>30 mV). Moreover, the ZChNCs-GO nanohybrids have reached a maximum Zeta potential up to −80 mV, which can be explained by the ionization of excess carboxyl groups on the surface of ZChNCs. Besides, the electrostatic regulation endows the nanohybrids with rheological behavior, which is beneficial to the macro assembly of liquid nanomaterials. This work provides a new class of hybrid colloidal nanomaterials, opens the structural design dimension of macro assembly and holds great potentials in high-performance biodegradable material.

The fate of aggregated graphene oxide upon the increasing of pH: An experimental and molecular dynamic study

Given the possible ecological dangers of graphene oxide (GO), a thorough understanding of its aggregation behavior is essential. During industrial applications, GOs may be used as multi-layered, and there is some possibility that GOs are released into the water environment in the aggregated state. Thus, elucidating the fate of aggregated GO is valuable for evaluating their environmental fate. In this work, the effect of pH on the fate of aggregated graphene oxide (GO) was explored using experimental measurements and molecular dynamic simulations and promoted aggregation of GO upon the increase of pH was observed. Additional investigations show that the presence of oxidation debris (ODs) on GO served as the primary driver of the unanticipated trend in aggregation behavior. GO consists of lightly oxidized functionalized graphene sheets and highly oxidized ODs. Upon the increase of pH and the deprotonation of functional groups, ODs are stripped from GO due to electrostatic repulsions and steric hindrance of water molecules. The stripping of ODs decreased the zeta potential and increased the hydrophobicity of GO, thus accelerating the aggregation. Additionally, the stripped ODs may recombine to GO edges and bridged GOs, which also contribute to further aggregation. Functional group deprotonation, ODs stripping, OD bridging, double layer compression, and charge neutralization all worked together to promote aggregation, resulting in the formation of FG-water-OD aggregates. Overall, the presence of ODs complicates the structures and properties of GO and should be considered during the development of GO-related nanomaterials and the evaluation of their environmental impact.

Determination of trace levels of uranium in waste solutions by energy dispersive X‐ray fluorescence following adsorption on graphene oxide

AbstractThis paper proposes a rapid X‐ray fluorescence (XRF)‐based screening method for the determination of trace uranium in solutions. In this method, uranium present in a solution was adsorbed onto graphene oxide (GO), which was collected and subjected to XRF analysis. Upon increasing the sodium ion concentration, the aggregation of GO was promoted, facilitating its collection. Since the GO‐collecting membrane filter was significantly larger than the X‐ray irradiation field of the XRF spectrometer, it was folded to 1/3 of its original length and width. The folded membrane filter was sealed to prevent uranium from contaminating the device and to ensure that the folded membrane filter was sufficiently thin. Subsequently, the amount of sodium perchlorate added to the sample solution was optimized to attain a salinity meter reading of 3%. The minimum detection limit (MDL) for uranium using this method was 0.37 ng ml−1, and the time required to simultaneously analyze six samples was approximately 2 h. Converting the MDL to the radioactivity concentration under conservative conditions generated a value of 0.037 mBq cm−3. To demonstrate the applicability of this method, a standard seawater sample was subjected to analysis, and the uranium concentration determined using our calibration curve agreed with the actual value within a margin of error. Therefore, the proposed method is suitable for screening numerous uranium‐contaminated water samples of small volumes.

UV-induced simultaneous removal of GO and U(VI): The role of aggregation, photo-transformation, adsorption and reduction

The photo-transformation of graphene oxide (GO) nanosheet and the photo-reduction of uranyl ion (U(VI)) have been widely studied separately. However, little attention has been given to the simultaneous photo-degradation of GO nanosheets and the photochemical reduction of U(VI) under ultraviolet (UV) illumination. In this study, the relationships among the UV-induced degradation of GO, the U(VI)-induced aggregation of GO, the adsorption of U(VI) on GO, and the UV-induced reduction of U(VI) as well as their roles in the UV-induced simultaneous photo-degradation of GO and photo-reduction of U(VI) were elucidated. These results indicated that the UV-induced transformation of GO occurred more quickly than the adsorption of U(VI) on GO. The presence of low concentration of U(VI) could promote the UV-induced transformation of GO at the initial stage, while UV irradiation weaken the efficiency of U(VI) ions in destabilizing GO nanosheets at the subsequent stage. Our findings are crucial for developing a highly efficient method to accomplish the simultaneous removal of GO and U(VI) in the actual environmental cleanup.

Fabricating high-loading ultra-small PtCu3/rGO via a traceless protectant and spray-freeze-drying method

Exploring excellent catalysts for oxygen reduction reaction (ORR) with a facile and cost-effective method is desirable but remains challenging. Herein, ultra-small PtCu3 nanoparticles (ca. 2.7 nm), immobilized on reduced graphene oxide (rGO), were synthesized via a novel and general strategy. Traceless protectant, NH4OH, was used to resist the aggregation of graphene oxide (GO), and the spray-freeze-drying method ensures excellent dispersion of the Pt and Cu precursors, which could not be achieved by other reported drying methods. After annealing, the nanoparticles with the highest mass loading, 52%, among reported ordered Pt-based catalysts were obtained. The PtCu3/rGO shows a remarkable electrocatalytic performance. Density functional theory calculations elucidate that PtCu3 possess a lowered energy barrier of the rate-determining step, contributing to significantly improved ORR kinetics. This strategy was extended to the synthesis of other binary- and quaternary-metallic Pt-based nanoparticles, which proved its generality and applicability towards the potential commercialization of fuel cell technologies.