Dataset for hierarchical tetramodal-porous architecture of zinc oxide nanoparticles microfluidically synthesized via dual-step nanofabrication

Zinc oxide (ZnO) nanoparticles (NPs) have been applied as high-performance intelligent materials to create a hierarchical multimodal-porous architectures for application in biomedical research fields [1]. They were microfluidically synthesized via dual-step nanofabrication compared to the conventional particles including ZnO NPs synthesized at single-pot macroscale, nanosized ZnO, and hybrid ZnO. The physicochemical properties were characterized, including morphology, particle size distribution, atomic composition, crystallinity, purity, reactant viscosity, surface charge, photocatalysis, photoluminescence, and porosity. A hierarchical multimodal-porous three-dimensional (3D) architecture of ZnO NPs was generated and optimized on the solid plate substrate of cellulose paper sheet after solvent evaporation. The dataset provides the nanomaterial design and architecture generation of ZnO NPs, explaining multi-physics phenomena in association with performance optimization processes.


Specifications
Materials Science: Nanotechnology Specific subject area Nanoparticle synthesis, Surface modulation, and Characterization Type of data Table  Image Graph Figure  How  Raw and analyzed Parameters for data collection Zinc oxide (ZnO) nanoparticles (NPs) were microfluidically synthesized and further solidified comparing with single-pot ZnO synthesis at macroscale. Nanosized and multiscale ZnO particles were also used as conventional products.

Description of data collection
Physicochemical characterization was performed in terms of morphology, particle size distribution, atomic composition, crystallinity, purity, reactant viscosity, surface charge, photocatalysis, photoluminescence, and porosity. Hierarchical multimodal-porous architecture and texture of zinc oxide (ZnO) nanoparticles (NPs) were analyzed after dropping serially on solid plate substrate of cellulose filter paper.

Value of the Data
• Microfluidically synthesized zinc oxide (ZnO) nanoparticles (NPs) generate hierarchical multimodal-porous three-dimensional (3D) architecture for advanced biomedical applications. • Physicochemical characterization provides the design information of ZnO NPs and their architectures, based on the theoretical and experimental analyses of the dataset.
• Researchers, such as physicists, chemists, biologists, (bio)engineers, and clinicians, can have of particular interest to use the dataset for comparison with other ZnO materials and the further explanation of fabrication and architecture generation. • The dataset can be beneficial for the development of fundamental NP evaluation protocols regarding the characterization of physicochemical properties and generation of 3D architecture of NPs with hierarchical multimodal porosity.

Data Description
Zinc oxide (ZnO) nanoparticles (NPs) have been explored as multifunctional nanomaterials finding applications in advanced biomedical research fields 2 , 3 . Their hierarchical porosity with multi-modality of micropores ( < 2 nm), mesopores (2-50 nm), and macropores ( > 50 nm) can be designed to enhance their performance in sensing, energy harvesting, and photocatalysis when used in medical devices and therapeutics, due to advanced mass transfer and exchange 4 , 5 . Currently, ZnO NPs can be synthesized using physical, chemical, and biological methods to meet the required characteristics regarding morphology, particle size distribution, crystallinity, purity, surface charge, photocatalysis, photoluminescence, and porosity [6] . A microfluidic device (MFD) is an advanced equipment in a miniaturized lab system for the sophisticated and controllable synthesis of ZnO NPs [7 , 8] . MFD integration into conventional methods can be beneficial for engineered NP generation accompanied with the designed and targeted physicochemical characteristics. Microfluidically synthesized ZnO NPs present hierarchical porosity with tetra-modality generating three-dimensional (3D) architecture, compared to the conventional particles of ZnO NPs synthesized using single-pot at macroscale, nanosized ZnO (nano-ZnO), and multiscale ZnO (hybrid-ZnO) [1 , 8] . Fig. 1 shows a microfluidic chemical reactor chip used for the microfluidic synthesis of ZnO NPs providing microflow with heat transfer within microfluidic channels. In the microfluidic   Table 1 ) was used as a control nanomaterial compared to MFD-2 ZnO. chemical reactor chip, there were three inlets and one outlet with a long serpentine channel connected to a syringe pump controlling at 0.1 mL min −1 . Its total volume was sized at 250 μL. Fig. 2 gives morphology and particle size distribution of MFD-1 ZnO using FE-SEM with EDS, which presented one of formulae for developing microfluidically synthesized ZnO NPs. MFD-1 ZnO was synthesized with Zn(acac) 2 in oleylamine at 1.67% (3 mL) for optimizing the microfluidic synthesis formulae of ZnO NPs. Fig. 3 displays the purity of microfluidically synthesized ZnO NPs, specifically MFD-2 ZnO, using FT-IR spectroscopy. MFD-2 ZnO was developed at 2.5% of Zn(acac) 2 in oleylamine. After the ethanol rinsing of ZnO NPs in a dual-step synthesis process, the purity after the maximum removal of residual amines was confirmed in the FT-IR spectra. Zn(acac) 2 , oleylamine, and Exp.10 ZnO of single-pot ZnO synthesis at macroscale in a Box-Behnken design (See Table 1 ) were compared with MFD-2 ZnO. Fig. 4 offers the viscosity of Zn(acac) 2 in oleylamine at 2.4%, 3.6%, and 7.1% (w v −1 ) at 20 °C and 30 °C as a controllable factor for the microfluidic synthesis of ZnO NPs, predicting the mi- croflow in the internal microfluidic channel of the chip. The image presents the Zn(acac) 2 solutions in oleylamine. Fig. 5 provides 3D surface plots illustrating reactant interactions affecting the particle size, morphology, and atomic composition of ZnO NPs during single-pot synthesis at macroscale based on the Box-Behnken design formulae (See Table 1 ). Fig. 6 presents the FE-SEM images, particle size distribution plots, and EDS spectra of representative ZnO NPs after single-pot synthesis at macroscale suggesting their morphology, particle size distribution, and atomic composition. The formulae at 1, 3, 9, and 15 of run orders among experimental order numbers in Box-Behnken design (See Table 1 ) are displayed (Exp.1, Exp.3, Exp.9, and Exp.15 ZnOs).  Fig. 7 shows the FE-SEM images, particle size distribution plots, and FE-TEM images of conventional ZnO particles including ZnO NPs at 10 of the experimental run order synthesized using single-pot at macroscale (Exp.10 ZnO, See Table 1 ), nano-ZnO, and hybrid-ZnO. Exp.10 ZnO was synthesized with 0.225 g of Zn(acac) 2 and 3.5 mL of oleylamine, and rinsed with 150 mL of ethanol. They provide the morphology, particle size distribution, and crystal structure of conventional ZnO particles compared with those of microfluidically synthesized ZnO NPs. Fig. 8 presents the zeta potential distribution plot of MFD-2 ZnO with an average value of 9.02 mV. MFD-2 ZnO was suspended in ethanol and appropriately diluted with fresh ethanol to reach the operating intensity range for zeta potential measurement. Fig. 9 shows the XPS and Raman profiles of the MFD-2 ZnO and MFD-2 ZnO aggregates. MFD-2 ZnO aggregate powders were prepared after dripping the hexane suspensions of MFD-2 ZnO on a glass slide and drying at room temperature for 24 h.   Table 1 ) at experimental run orders 1, 3, 9, and 15 in the macroscale synthesis of ZnO NPs.   a collimated beam device (CBD). The photocatalytic degradation of methyl orange by MFD-2 ZnO and the aggregates were monitored under dual UV irradiation. Fig. 11 provides the photoluminescence (PL) of MFD-2 ZnO at the range of 0.75-6.0 mg mL −1 . The excitation wavelength was 358 nm, and the emission wavelength was at the range of 400-700 nm. Fig. 12 shows the immobilization of MFD-2 ZnO on a cellulose paper sheet depending on the NP ethanol wetting and NP amounts (0.625-5.0 mg). In association with NP ethanol wetting, two types of MFD-2 ZnO were used for immobilization on the cellulose paper sheet: dMFD-2 ZnO as the dried form and wMFD-2 ZnO as the ethanol-wetted form. Cellulose paper sheet photos and the FE-SEM images of immobilized MFD-2 ZnO on the cellulose paper sheet were obtained, providing information on the NP covering or hierarchical porous architecture generation of NP network.  Table 1 lists the single-pot synthesis of ZnO NPs at macroscale in Box-Behnken design to investigate each interaction of reactants and rinsing solvent for synthesis of ZnO NPs. The independent variables of Zn(acac) 2 , oleylamine, and ethanol were selected as 0.05-0.4 g, 1.0-6.0 mL, and 50-250 mL, respectively, for 15 experiments. Table 2 presents the surface characteristics, such as pore size (nm or Å ), pore volume (cm 3 g −1 ), and surface area (m 2 g −1 ) of MFD-2 ZnO compared to those of Exp.10 ZnO (See Table 1 ), nano-ZnO, and hybrid-ZnO after mesopore and micropore analyses based on Brunauer-Emmett-Teller (BET) theory. Table 3 lists the atomic composition of MFD-2 ZnO compared to those of conventional ZnO particles including Exp.10 ZnO (See Table 1 ), nano-ZnO, and hybrid-ZnO monitored in the EDS profiles.

Microfluidic synthesis of ZnO NPs in a chemical reactor chip via dual-step nanofabrication
Intrinsic nanoporous ZnO NPs were nucleated and solidified via dual-step reactions of zinc acetylacetonate hydrate [Zn(acac) 2 ] (Sigma) and oleylamine (3 mL; 1.67% for MFD-1 ZnO, 2.5% for MFD-2 ZnO, and 5.0% for MFD-3 ZnO, w v −1 ) in a microfluidic process (microfluidic chem-  Fig. 12. Immobilization of MFD-2 ZnO on cellulose paper sheet at 0.625-5.0 mg. Two types of ZnO NPs were used: dMFD-2 (dried) and wMFD-2 (ethanol-wetted) ZnOs. The cellulose paper sheet and FE-SEM images were obtained after immobilization. MFD-2 ZnO covered the solid plate substrate surface or generated the hierarchical porous architecture depending on NP ethanol wetting and amounts. Specifically, the wMFD-2 ZnO started forming the hierarchical porous architecture at 0.625 mg.  ical reactor chip, Dolomite, Blacktrace Holdings Ltd., Royston, UK) at 80 °C for 30 min, along with a further heating process at 150 °C for 1 h. Preheating, mixing, and synthesis processes were continuously performed in the MFD. The flow rate was 0.1 mL min −1 controlled using a syringe pump. After cooling to room temperature, the mixture was poured into ethanol (100 mL) and the resulting white precipitates were rinsed with ethanol (Merck), and dried. The premade aggregates of microfluidically synthesized ZnO NPs were generated after dripping the NP suspensions in hexane (Sigma) on glass slide and drying at room temperature for 24 h.

Field emission-scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS)
Morphology was monitored using field emission-scanning electron microscopy (FE-SEM, S-4300SE, Hitachi, Co. Ltd., Japan) operated at an acceleration voltage of 15.0 kV. Particle size dis-tribution was displayed from obtained FE-SEM images using ImageJ (NIH). EDS analysis was also performed on the particle surface to quantitatively determine the element composition.

Fourier-transform infrared (FT-IR) spectroscopy
The removal of residual amines from ZnO NPs was determined by FT-IR spectroscopy. The powdered samples were mixed with potassium bromide (KBr) and subjected to a pressure to produce a disc. IR spectra region at 3,80 0-60 0 cm −1 were recorded on a FT-IR vacuum spectrometer (Bruker Vertex 80v, Bruker Optics, Inc., Billerica, MA, USA). For each spectrum, the frequencies for all sharp bands were accurate to 0.01 cm −1 .

Zeta potential measurement
Zeta potential values of ZnO NPs were measured at room temperature using a light scattering (ELS-Z, Otsuka Electronics Co., Ltd., Tokyo, Japan) with standard cell. ZnO NP dispersions in ethanol were diluted with fresh ethanol prior to analysis to reach the appropriate intensity for the measurements. Huckel equation was used to calculate zeta potential values for conversion, and the average zeta potential (mV) was determined in ELS-Z software (Otsuka Electronics Co., Ltd.).

X-ray photoelectron spectroscopy (XPS)
The atomic compositions of ZnO NPs and the aggregates were determined using XPS (K-Alpha, Thermo Scientific, Thermo Fisher Scientific Inc., Hillsboro, OR, USA) with a monochromated Al K-alpha source.

Raman spectroscopy
ZnO NPs and aggregates were placed on a glass slide and were subjected to Raman spectrometry (Horiba LabRam HR Evolution, Horiba, Ltd., UK) with a laser (wavelength, 532 nm). Raman spectra were recorded with five acquisitions and three accumulations.

Ethics Statement
The work does not involve the subject of humans, animals, or data from social media platforms.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships which have or could be perceived to have influenced the work reported in this article.

Data Availability
Dataset for hierarchical tetramodal-porous architecture of zinc oxide nanoparticles microfluidically synthesized via dual-step nanofabrication (Original data) (Mendeley Data).