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Facile and Green Synthesis of Palladium Nanoparticles-Graphene-Carbon Nanotube Material with High Catalytic Activity
Facile synthesis of Pd@graphene nanocomposites with enhanced catalytic activity towards Suzuki coupling reaction
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D. Hassen, M. A. Shenashen, … S. A. El-Safty
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Sea-Island-Like Morphology of CuNi Bimetallic Nanoparticles Uniformly Anchored on Single Layer Graphene Oxide as a Highly Efficient and Noble-Metal-Free Catalyst for Cyanation of Aryl Halides
Gopiraman Mayakrishnan, Vijayakumar Elayappan, … Ill-Min Chung
Facile and scalable production of heterostructured ZnS-ZnO/Graphene nano-photocatalysts for environmental remediation
Sunil P. Lonkar, Vishnu V. Pillai & Saeed M. Alhassan
In situ decoration of Au NPs over polydopamine encapsulated GO/Fe3O4 nanoparticles as a recyclable nanocatalyst for the reduction of nitroarenes
Saba Hemmati, Majid M. Heravi, … Hojat Veisi
Tai Sun1,
Zheye Zhang1,
Junwu Xiao1,
Chen Chen1,
Fei Xiao1,
Shuai Wang1,2 &
Yunqi Liu3
Scientific Reports volume 3, Article number: 2527 (2013) Cite this article
Porous materials
Self-assembly
Synthesis of graphene
We report a facile and green method to synthesize a new type of catalyst by coating Pd nanoparticles (NPs) on reduced graphene oxide (rGO)-carbon nanotube (CNT) nanocomposite. An rGO–CNT nanocomposite with three-dimensional microstructures was obtained by hydrothermal treatment of an aqueous dispersion of graphene oxide (GO) and CNTs. After the rGO–CNT composites have been dipped in K2PdCl4 solution, the spontaneous redox reaction between the GO–CNT and PdCl42− led to the formation of nanohybrid materials consisting rGO–CNT decorated with 4 nm Pd NPs, which exhibited excellent and stable catalytic activity: the reduction of 4-nitrophenol to 4-aminophenol using NaBH4 as a catalyst was completed in only 20 s at room temperature, even when the Pd content of the catalyst was 1.12 wt%. This method does not require rigorous conditions or toxic agents and thus is a rapid, efficient and green approach to the fabrication of highly active catalysts.
Noble metal nanoparticles (NPs) have attracted considerable attention because of their excellent catalytic properties and their potential applications, which include organic synthesis, fuel cells and environmental protection1,2,3. Because the high surface energy of NPs usually causes extensive aggregation4,5,6,7, stabilizers and supporting materials have typically been used to obtain homogeneously distributed samples8,9,10,11. The former method requires capping agents that may severely limit the catalytic activity. Therefore, the use of high-surface-area materials as supports is a promising strategy for the preparation of ultrafine and well-defined noble-metal NPs that not only function as barriers to prevent encapsulated NPs from coalescing but also improve the chemical and thermal stability and enhance the electrical conductivity of functional materials. Various noble metal based catalytic systems have been developed, such as Au@ZrO2, Au@Carbon and Pt-decorated carbon composites12,13,14. For example, the Au@Carbon core-shell catalyst exhibits excellent catalytic properties and it can catalyze the reduction of 4-nitrophenol (4-NP) by NaBH4 to 4-aminophenol (4-AP) within 5 min at room temperature13. The facile and green synthesis of novel metal-NP catalysts that exhibit further improved catalytic activity remains a challenge.
In this work, we fabricated a high-performance Pd–rGO–CNT nanocomposite catalyst by depositing Pd NPs onto a reduced graphene oxide (rGO)–carbon nanotube (CNT) support. We synthesized a three-dimensional (3D) porous rGO–CNT hydrogel by hydrothermally treating an aqueous dispersion of graphene oxide (GO) and CNTs. We obtained the Pd–rGO–CNT composites by dipping the rGO–CNT composites into aqueous solutions of K2PdCl4 for a few minutes. Pd NPs with a uniform size of 4 nm were grown in situ on GO–CNT scaffolds by the spontaneous redox reaction between a noble-metal precursor and carbon materials. The ideal combination of Pd NPs and the 3D rGO–CNT framework provides the resultant Pd–rGO–CNT hybrid with integrated properties, such as large surface area, high loading of catalytic NPs and good stability and durability. Therefore, the as-prepared nanohybrid exhibited remarkably high and stable catalytic activity toward the reduction of 4-NP. The reduction of 4-NP by NaBH4 to 4-AP was completed within 20 s at room temperature. The catalyst was easily separated from the product and was reused directly. As far as we know, this material is the most effective nanohybrid catalyst for 4-NP reduction. Our method offers several advantages in terms of easy scale-up, environmentally friendliness and low cost. We envision that the broad application of this strategy will contribute to the development of the next generation of advanced catalytic materials.
The synthetic route for the Pd–rGO–CNT composite is shown in Fig. 1. GO prepared via the Hummer method contains a large number of oxygen-containing functional groups, which allow GO to be well-dispersed in an aqueous solutions15. The amphiphilic nature of GO sheets can serve as surfactant; CNTs can be dispersed into individual ones after ultrasonication and adsorbed onto the GO surface through π–π attractions16. Hydrothermal treatment of the GO and CNT aqueous dispersion leads to the formation of macroscopic rGO–CNT cylinder hydrogels via weak interactions, such as van der Waals forces, hydrogen bonding, π–π stacking and inclusion interactions (Fig. S1). These hydrogels have well-defined and interconnected three-dimensional (3D) porous network and the pore walls consist of thin layers of stacked rGO sheets (Fig. 2a). The partial coalescing or overlapping of graphene sheets results in the formation of cross-linking sites of the framework of hybrid and the pore sizes of the network are in the range of several submicrometer to micrometers. The CNTs are uniformly distributed between the graphene sheets. The surface area of the 3D rGO–CNT material was 307 m2g−1, which is greater than that of the 3D rGO material (201 m2g−1) obtained by fitting the isotherm to the Brunauer–Emmett–Teller (BET) model (Fig. S2). This increased surface area is ascribed to the synergistic effects between the graphene and CNTs in the rGO–CNT nanocomposite. During the self-assembly process of rGO–CNT hydrogels, rGO easily forms agglomerates due to the π–π interactions between individual graphene nanosheets. The insertion of hierarchical tortuous CNTs in rGO–CNT nanocomposites can bridge the adjacent graphene nanosheets, prevent graphene sheets from restacking and increase the specific surface area.
Schematic illustration of the synthesis of the Pd–rGO–CNT composite.
SEM and TEM images of Pd–rGO–CNT composite.
(a) SEM image of Pd–rGO–CNT hybrid. (b–d) TEM images of Pd–rGO–CNT hybrid. (e) The selected-area electron diffraction (SAED) pattern and (f) XRD patterns of Pd–rGO–CNT composite.
The Pd–rGO–CNT composite was obtained via a redox reaction between the rGO–CNT composites and a K2PdCl4 aqueous solution in an ice bath. During this process, the 3D-structured rGO–CNT hydrogel not only increases the specific contact area, which facilitates transport of the Pd2+ ions and electrons into the inner region of the graphene sheets, but also provides more exposed active sites for the anchoring of Pd precursors and for Pd nucleation. Transmission electron microscopy (TEM) images revealed that Pd NPs with a uniform size of 4 nm were well-dispersed on the surfaces of the rGO–CNT scaffolds (Figs. 2b–d). The corresponding particle size distribution histogram of Pd nanoparticles is shown in Fig. S3. The interplanar spacings for the lattice fringes of Pd were 0.223 nm and 0.195 nm, which correspond to the (111) and (200) lattice planes, respectively, of the face-centered cubic (fcc) Pd structure (Fig. 2d). The selected-area electron diffraction (SAED) pattern corresponds to the (111), (200), (220) and (311) planes of the expected fcc Pd (Fig. 2e). XRD patterns and the corresponding standard line of Pd are shown in Fig. 2f. The strongest reflection of the rGO–CNT composite is the (002) reflection at 2θ = 25.9°, which also proves that the Pd NPs exhibit an fcc pattern typical of Pd metal. In addition, X-ray energy dispersive spectroscopy (EDS) spectra further confirm the presence of metallic Pd (Fig. S4).
Quantitative information related to the chemical state, type and extent of the surfaces of the GO–CNT, rGO–CNT and Pd–rGO–CNT are investigated by X-ray photoelectron spectroscopy (XPS), as shown in Fig. 3. Typically, the peaks at 284.6, 286.6 and 288.2 eV are assigned to the C−C, C−O and C = O bonds, respectively. The peak intensity of the C−O bond in GO was the most intense (54.57%), due to the presence of oxygen-containing functional groups (Figs. 3b–d). After the hydrothermal reduction process, the peak intensity of the C–O bond decreased to 17.72% (Fig. 3c). Furthermore, after the sample was immersed in the K2PdCl4 solution, the peak intensity of the C–O bond increased from 17.72% to 21.96% and peaks corresponding to the binding energies of the binding energies of Pd 3d5/2 and 3d3/2 (335.2 and 340.2 eV, respectively) appeared (Fig. S5). Quantitative analysis of the XPS spectrum provided compelling evidence that the Pd content in the Pd–rGO–CNT composite is 1.33 wt%, as shown in Supporting Information (Table S1). In addition, the Pd content was determined using microwave plasma-atomic emission spectrometer (MP-AES). The results showed that the Pd concentration in Pd–rGO–CNT is 1.12 wt%, which is approximately consistent with the concentration obtained from the XPS spectrum. These results suggest that the nucleation of a Pd particle on rGO–CNT is attributed to the direct redox reaction between the metal ions and the rGO–CNT composite. According to the previous studies, the Fermi Level, which is equivalent to the electrochemical potential of electrons in a redox system of CNT, is approximately about +0.5 V vs SHE17,18,19 and the reduction potential of rGO is less than 0.25 V vs SHE20,21, both of these potentials are lower than the reduction potential of PdCl42− (+0.6 V vs SHE). Therefore, rGO/Pd2+ and CNT/Pd2+ systems undergo spontaneous oxidation and reduction in solution.
(a) X-ray photoemission spectroscopy (XPS) profiles of GO–CNT, rGO–CNT and Pd–rGO–CNT hybrid samples. (b) Curve fit of the C1s peak of GO–CNT. (c) Curve fit of the C1s peak of rGO–CNT. (d) Curve fit of C1s peak of Pd–rGO–CNT.
We evaluated the catalytic ability of the as-synthesized Pd–rGO–CNTs in the reduction of 4-NP to 4-AP by NaBH4 in an aqueous medium22,23. The addition of Pd–rGO–CNT caused fading and ultimately bleaching of the yellow color of the 4-NP in aqueous solution. The absorption of 4-NP at 400 nm decreased rapidly, with a concomitant increase in the intensity of a new peak at 300 nm in UV-Vis spectra; this peak was assigned to 4-AP (Fig. 4). Whereas reactions in the presence of Au/Carbon core–shell and Au/SiO2 microspheres as catalysts were completed in 300 s and 1 h, respectively, the reduction with the Pd–rGO–CNT composite as catalyst could be performed in only 20 s, even though the Pd content of the catalyst was as low as 1.12 wt%. We investigated the stability of Pd–rGO–CNT by performing the same reduction reaction with the same catalyst 20 times. This catalyst also exhibited high activity after 20 successive cycles of reactions, with 100% conversion within a reaction period of 40 s, which exceeds the performance of the Au/carbon core–shell and the Au/SiO2 systems. In the presence of the Au/carbon core–shell and the Au/SiO2 microsphere catalysts, the reduction reactions were completed in 300 s and 1 h, respectively (Table 1). We evaluated the stability of the Au@carbon catalyst by performing the same reduction reaction five times. The conversion was close to 100% within a reaction period of 5 min.
Table 1 Comparison of the catalytic recycling stabilities of composites
(a) UV-Vis spectra of 4-NP reduction (i) before and (ii) 20 s after the addition of the Pd–rGO–CNT composite. (b) The stability of the catalyst during 20 cycles of the same reduction reaction.
Such excellent catalytic performance of Pd–rGO–CNT nanocomposite is related to its 3D macrostructures. During hydrothermal treatment, the conjugated structure of the rGO sheets and the CNTs provide stacking sites on which 3D macrostructures are formed. This architecture with its unique conductive carbon networks is an effective scaffold for the deposition of Pd NPs Well-defined Pd NPs that are highly dispersible and have an ultrasmall size can grow in situ on a 3D rGO–CNT framework through the direct redox reaction between metal ions and the rGO–CNT composite, which is the most important issue for improving the catalytic performance and realizing the application of Pd–rGO–CNT nanomaterials.
To demonstrate the advantages of the Pd–rGO–CNT material, macroscopic rGO, rGO–CNT and Pd–rGO composites with porous structures were also synthesized for comparison (Fig. S6). Whereas pristine carbon materials, including rGO and rGO–CNT, exhibited no catalytic properties, the Pd–rGO nanocomposite demonstrated lower catalytic activity and stability than the Pd–rGO–CNT nanocomposite. The reaction time increased from 30 s to 210 s after five successive cycles of reactions when Pd–rGO nanocomposite was used as the catalyst. Therefore, the introduction of CNTs is thought to effectively improve the electron-transfer rate24,25, to provide sufficient space and sites for the redox reaction of 4-NP to 4-AP by NaBH4 and to accelerate the reduction rate. At the same time, the microstructure of the rGO–CNT architecture prevents the aggregation of Pd NPs. The resultant Pd–rGO–CNT nanocomposite possesses a large surface area, high mechanical strength and excellent durability; it consequently exhibits remarkably high, stable catalytic activity.
In summary, we developed a facile and green method for the synthesis of 3D Pd–rGO–CNT nanocomposites and explored their practical application in catalysis. This new type of catalyst was synthesized through hydrothermal treatment of an aqueous dispersion of GO and CNT, followed by spontaneous redox reaction between Pd2+ and an rGO–CNT hybrid to form Pd NPs decorated with rGO–CNT microporous materials. The resultant Pd–rGO–CNT nanocomposites possess a unique large surface area, an extremely high aspect ratio, high mechanical strength and excellent durability and therefore exhibit remarkably high and stable catalytic activity toward the reduction of 4-NP. These features, coupled with the simplicity of the assembly process, the suitability of the method for large-scale production and the green synthesis approach, allow a variety of industrial applications in environmental protection, electrocatalysis, biomedical applications and sensors.
Preparation of GO
GO was synthesized by the modified Hummers method15. Briefly, 10 g of natural graphite and 5 g of NaNO3 were added to 230 ml of concentrated sulfuric acid under stirring in a flask immersed in an ice-water bath. Then, 30 g of KMnO4 was added slowly and the mixture was stirred at 30°C for 2 h. Next, 460 ml of distilled water was added and the mixture was further stirred for 30 min at 95°C. Finally, 940 ml of distilled water and 30 ml of H2O2 (5%) were subsequently added to terminate the reaction and the color of the solution turned from dark-brown to yellow. The generated solid graphite oxide was separated by centrifugation, washed and dried under vacuum.
Self assembly of rGO-CNT hydrogel
The material was prepared by the addition of 30 mg of CNTs to a 2 mg/ml homogeneous GO aqueous dispersion (the mass ratio of GO to CNT was 2:1) under sonication for approximately 30 min. The mixture was subsequently sealed in a 50-ml Teflon-lined autoclave and maintained at 180°C for 12 h. After the mixture was cooled in room-temperature air with natural convection, a black gel-like 3D cylinder was obtained. The size of the hydrogel could be freely adjusted by changing the volume of the GO aqueous dispersion. The as-obtained samples were freeze-dried overnight for use in subsequent experiments. The 3D rGO hydrogel was fabricated by the same method but without the addition of CNTs.
Synthesis of Pd-rGO-CNT nanocomposite
One milliliter of a K2PdCl4 (10 mM) aqueous solution and 5 mg of rGO–CNT composite were added to a 10-ml aqueous solution and maintained in a vial under vigorous stirring for 30 min in an ice bath. Afterwards, the reaction mixture was washed three times with pure water and centrifuged to remove the remaining reagents. The Pd–rGO nanocomposite was synthesized using a similar procedure.
Catalytic study
4-Nitrophenol (3 ml, 0.1 mM) was mixed with a freshly prepared aqueous solution of NaBH4 (0.1 ml, 0.3 M). Different catalysts (5 mg) were then added under constant magnetic stirring. UV-Vis absorption spectra were recorded to monitor the change in the reaction mixture.
Natural graphite powder was purchased from Alfa Aesar (USA); multi-walled carbon nanotubes (CNTs) were purchased from XF NANO (China); K2PdCl4 (99%), 4-nitrophenol (>99%) and NaBH4 (96%) were purchased from Sinopharm Chemical Reagent Co. (China) and were used directly without further purification. All other chemicals used were of analytical reagent grade. Ultra-pure water (18 MΩ·cm) for solution preparation was produced using an Aquapro System (China). Scanning electron microscopy (SEM) images were obtained on an FESEM instrument (GSM6510LV, JEOL, Japan). Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images were obtained using a TECNAI G2-20 U-Twin instrument (Netherlands) operated at an acceleration voltage of 200 kV. The samples of composites were suspended in ethanol and were prepared by being drop-cast onto a carbon-coated 200-mesh copper grid and subsequently dried at room temperature. X-ray photoelectron spectroscopy (XPS) measurements were performed on a VG ESCALAB 250 spectrometer (UK) using an Al Kα X-ray source (1486 eV), X-ray radiation (15 kV and 10 mA) and hemispherical electron energy analyzer. All of the binding energies were calibrated according to the reference energy of C1s (C1s = 284.6 eV). X-ray powder diffraction (XRD) measurements were performed on a diffractometer (X′ Pert PRO, Panalytical B.V., Netherlands) equipped with a Cu Kα radiation source. The Pd content was determined using a microwave plasma-atom emission spectrometer (MP-AES, Agilent 4100, USA). UV-Vis measurements were conducted on a Specord 50 UV-Vis spectrophotometer (Germany). Nitrogen adsorption/desorption isotherms were obtained at 77 K on an accelerated surface area and porosimetry system (ASAP 2020, USA) to measure the surface area of the films using the Brunauer–Emmett–Teller (BET) method.
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This research was financially supported by the National Natural Science Foundation of China (Project No. 51173055).
School of Chemistry & Chemical Engineering, Huazhong University of Science and Technology, Wuhan, 430074, P.R. China
Tai Sun, Zheye Zhang, Junwu Xiao, Chen Chen, Fei Xiao & Shuai Wang
State Key Lab of Digital Manufacturing Equipment & Technology, School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan, 430074, P.R. China
Shuai Wang
Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, P.R. China
Yunqi Liu
Tai Sun
Zheye Zhang
Junwu Xiao
Chen Chen
Fei Xiao
T.S., Z.Z. and J.X. contributed equally. T.S., F.X., S.W. and Y.L. proposed, planned and designed the project. T.S., Y.Z. and C.C. performed the material preparation, characterizations and catalytic tests. All authors contributed to writing the manuscript.
Supplementary information-Facile and Green Synthesis of Palladium Nanoparticles-Graphene-Carbon Nanotube Porous Material with High Catalytic Activity
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareALike 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/
Sun, T., Zhang, Z., Xiao, J. et al. Facile and Green Synthesis of Palladium Nanoparticles-Graphene-Carbon Nanotube Material with High Catalytic Activity. Sci Rep 3, 2527 (2013). https://doi.org/10.1038/srep02527
DOI: https://doi.org/10.1038/srep02527
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Tag Archives: halloween books
Peanut Butter & Brains by Joe McGee and Charles Santoso
Judging from the success of The Walking Dead and the hilarious Zombieland that I finally got around to watching recently, zombies have become pretty mainstream fare. Thus, it might come as no surprise that they have also entered the realm of picture books.
No Such Thing by Jackie French Koller and Betsy Lewin
When his family moves into an old house, Howard can't sleep because he thinks there's a monster under his bed, even though his mom insists there's no such thing. Meanwhile, under Howard's bed, a "non-existent" little monster is afraid because he hears a boy above his bed, but HIS mom is adamant that there's no such thing!
The Curious Little Witch by Lieve Baeten
Lizzy and her cat are flying around on her broomstick when they spot a house with the lights still on. Being a curious little witch, she can't resist taking a peek but accidentally crashes inside.
Vampire Baby by Kelly Bennett and Paul Meisel
When two sharp canine teeth appear in little Tootie's mouth, seemingly overnight, the adorable toddler turns into a serial biter who sinks her "fangs" everywhere — and unfortunately for her big brother, she seems to find him particularly tasty… *Youch!* Could it be that she's really a vampire baby?! (It sure doesn't help that she seems to favour blood-red food and sleeps really poorly at night…)
Dog and Bear: Tricks and Treats by Laura Vaccaro Seeger
We're more familiar with Laura Vaccaro Seeger's more artistically inclined books like Green and First the Egg, but these Dog and Bear books show that talented authors are capable of books that showcase a totally different — but just as awesome — side to them.
The Spider and the Fly by Mary Howitt and Tony DiTerlizzi
This isn't strictly a Halloween book, but I love its slightly creepy feel — kinda like one of those old black-and-white horror movie reels.
In this deceptively simple counting book, five creatures lurk around a "creepy haunted house" until they run into something apparently even scarier that sends them running.
The Haunted Hamburger by David LaRochelle and Paul Meisel
Ghost stories take on a whole new meaning in this wacky and highly original picture book.

redpajama_set_name: RedPajamaCommonCrawl


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Naomi Campbell casino plan sparks worry over rare Kenyan turtle
by Bogonko Bosire
Plans by supermodel Naomi Campbell to build a high-end casino near turtle sanctuaries in Kenya's Indian Ocean resort of Malindi have sparked a firestorm from conservationists and residents.
Apart from hosting a bevy of beauties and moneyed men, the six-star casino complex -- to be called Billionaires Resort -- could disrupt the hatching process of several rare species of turtles, they say.
Conservationists are worried that noise and lights from the casino envisioned by the British catwalk legend and her former boyfriend, Formula One boss Flavio Briatore -- who already owns one hotel in Malindi, will scare the turtles away.
Last month, Pierino Liana, the east and central Africa head of Briatore's Lion Group, announced the ex-couple had filed plans to build a multi-million dollar casino in Malindi, promising it would open up jobs for local residents, many of whom live below the poverty line.
"You have fabulous beaches and people here are just amazingly nice. But something needs to be put correct to attract big time investors," Campbell told the Standard daily while vacationing in Kenya in August, suggesting roads and the airport would also need to be upgraded.
Malindi Marine Association Director Athman Seif said the casino and the jet-setting guests it would draw would scupper years of painstaking work to protect the endangered marine creatures.
"It will be like destroying creatures that many people have invested a lot to protect," he told AFP. "If this is allowed, it will have massive repercussions: the noise from the casino (and) the lighting will affect the hatching of turtles, and tourists walking on the beach will step and destroy eggs and nests."
Female turtles hatch ashore and the baby turtles usually find their way back to the sea by looking for the brightest natural horizon. A glittering construction in the heart of Malindi's marine park could lure the hatchlings in the wrong direction and away from the beach, leading them to die of dehydration, the conservationists say.
"We are not against development, but all we are calling for is sustainable, low- environmental-impact and high quality tourism development," said Stephen Trott, who heads Local Ocean Trust, a Malindi-based turtle conservation group.
A Kenya Wildlife Service official who did not want to be named said the agency was keeping a close eye on the project.
Kenya Tourism Board chairman Jake Grieves-Cook was also cautious, noting that the casino project was still going through the planning application process -- which generally calls for environmental impacts and could take years before receiving final approval.
"We support any properly regulated development which abides by environmental regulations, but we need to ensure that our wildlife is conserved and protected. So any development should always pay careful attention to conservation issues," he told AFP.
Campbell and Briatore have been frequent visitors to the resort, which has long been popular with retired white settlers and became a hub for repentant Italian mafia informants in the 1980s.
In 2005, the 37-year-old Campbell publicly professed her adoration. "One of the reasons I love Malindi is that I can walk on the road without people bothering me. They just greet you with a smile and say hello," she said.
According to Malindi residents, Briatore has another hotel in the resort called White Elephant.
"Let them go improve the quality of White Elephant," said one resident. "We are totally against the casino. This is a small town, we have one casino and we don't want another one," said Terry Hill of the Malindi South Residents Association.
"Furthermore, we are told that they want to build near a marine park. Be sure we won't allow that because we are conservationists. Let them go and build it elsewhere," Hill said.
Seif warned that Malindi and the Kenyan coastline, which harbours many unique species, was in danger of being irremediably spoilt by mushrooming constructions.
"After all, we have enough hotels in coast region. We do not want anymore. The Kenyan coast is becoming a wall of hotels instead of a tranquil shoreline."
Related articles on global marine issues


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Battle House and 'Operation Horses and Heroes' team up on July 30th with a fundraiser for veterans with disabilities
By Denise Freese
Come out on July 30th with your friends and family and play laser tag to show your support for our veterans. Battle House will team up with Operation Horses and Heroes to host their largest fundraising event to date. Operation Horses and Heroes is a wonderful non-profit organization that provides equestrian therapy for disabled veterans. The group travels around the country with specialized therapists, who provide comfort and healing to veterans suffering from post-traumatic stress disorder (PTSD) and other afflictions caused from serving in the military.
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Doug and his family have had horses in the past, and currently have two miniature horses, Sophie and Cricket. Their love of horses gives even greater meaning to this opportunity to help Operation Horses and Heroes, which assists disabled veterans in numerous ways. "The Barrington community, where Battle House is located, is a 'horse community'," said Huckbody. "Our local customers will especially appreciate this opportunity to help our veterans, by raising funds for Operation Horses and Heroes." A portion of the day's proceeds will go directly to Operation Horses and Heroes. For more information about this special fundraiser on July 30th, and how you can help this fantastic organization, please contact:
Battle House Laser Combat
28039 W. Northpointe Pkwy, Lake Barrington, IL 60010
WWW.BattleHouseLaserCombat.com
www.operationhorsesandheroes.org


text:
package buildingblock.searching.lc240_searcha2dmatrix2;

import java.util.Arrays;

/**
 * Write an efficient algorithm that searches for a value in an m x n matrix.
 * This matrix has the following properties:
 * Integers in each row are sorted in ascending from left to right.
 * Integers in each column are sorted in ascending from top to bottom.
 * For example, consider the following matrix:
 * [
 *  [1,   4,  7, 11, 15],
 *  [2,   5,  8, 12, 19],
 *  [3,   6,  9, 16, 22],
 *  [10, 13, 14, 17, 24],
 *  [18, 21, 23, 26, 30]
 * ]
 * Given target = 5, return true.
 * Given target = 20, return false.
 */
public class Solution {

    public static void main(String[] args) {
        System.out.println(new Solution().searchMatrix(new int[][]{{-1, 3}}, 1));
    }

    // O(M+N) time. (Like how many nodes you went through in BST)
    // I found this matrix is like a Min/Max Heap if you start from 0,0 or m,n and
    // the only thing you know is current number is greater or smaller than both left and right "child".
    // But you don't know how to make decision of where to go.
    // However, if you start from m,0 or 0,n, the matrix looks like a Binary Search Tree.
    // Then the path of search is just like to traverse the BST until we reach the target node.
    public boolean searchMatrix(int[][] A, int target) {
        if (A.length == 0 || A[0].length == 0) return false;
        int m = A.length, n = A[0].length;
        int row = m - 1, col = 0;
        while (0 <= row && col < n) {
            if (A[row][col] == target) return true;
            if (A[row][col] < target) col++;
            else row--;
        }
        return false;
    }

    // O(MlogN) solution
    public boolean searchMatrix4(int[][] A, int target) {
        if (A.length == 0 || A[0].length == 0) return false;
        int m = A.length;
        for (int i = 0; i < m; i++) {
            if (Arrays.binarySearch(A[i], target) >= 0) return true;
        }
        return false;
    }

    // My 2AC: O(M+N) time
    // Integers in each row are sorted in ascending from left to right.
    // Integers in each column are sorted in ascending from top to bottom.
    public boolean searchMatrix2(int[][] matrix, int target) {
        if (matrix.length == 0 || matrix[0].length == 0) {
            return false;
        }
        int row = 0, col = matrix[0].length - 1;
        while (row < matrix.length && col >= 0) {
            if (matrix[row][col] > target) col--;
            else if (matrix[row][col] < target) row++;
            else if (matrix[row][col] == target) return true;
        }
        return false;
    }

    // My 1AC
    public boolean searchMatrix1(int[][] matrix, int target) {
        int n = matrix.length;
        if (n == 0 || matrix[0].length == 0) {
            return false;
        }

        int m = matrix[0].length;
        for (int i = 0; i < n; i++) {
            if (matrix[i][m - 1] < target) {
                continue;
            }

            if (Arrays.binarySearch(matrix[i], target) != -1) {
                return true;
            }
        }
        return false;
    }

}

redpajama_set_name: RedPajamaGithub


text:
Q: What type of encryption to use for 48-bit to 48-bit? I've got a bunch of 48-bit (6 byte) values that I need to encrypt symmetrically. The two requirements are:

*

*The resulting encrypted value needs to also be 48-bits (6 bytes) long. They key itself can be (and would preferably be) much longer to guard again brute force attacks.

*The resulting encrypted value needs to be deterministic, i.e. value A using key B will always produce encrypted value C (we encrypt on the fly and show the encrypted data to the user so need to always show the same value)
All block ciphers I've found have used a minimum block size of 64 and appear to be fixed (you can't use an arbitrary block size). Should I be thinking about a stream cipher?
I'm doing this in Java.
Note: I've seen this question and associated answers but wasn't clear on whether the suggestions would satisfy my 2nd requirement.

A: Consider format preserving encryption.

A: (Sorry, I originally misread the requirements thinking it was the INPUT data that needed to be 6 bytes.)
I don't think you can do exactly what you want with standard cryptographic algorithms:

*

*the problem with stream ciphers is that standard ones effectively work by generating a stream of pseudorandom bits from the key and then XORing these bits with the plaintext; effectively this means that you should never use the same stream of bits twice (e.g. if you do, then XORing two ciphertexts gives you the same result as XORing the corresponding plaintexts; and in any case with 48 bits, there are only 2^48 possible bitstreams, so you can just test them all by brute force);

*the problem with block ciphers is that there's no standard one as far as I'm aware that has a block size of 48 bits.

Now, that doesn't mean that a 48-bit block cipher couldn't be developed-- and indeed I dare say there are some out there-- just that none of the bog-standard ciphers that have undergone years of scrutiny from the cryptographic community have that block size.
So I would suggest options are:

*

*relax the requirement of a 48-bit ciphertext; for example, TripleDES has a 64-bit block size and is "fairly" secure (equivalent to 112 bit security)[*];

*in principle, you could implement your own block cipher with whatever block size you require, sticking as close as you can to a standard design, e.g. a Feistel network following some generally recommended design principles-- as a starting point, see Schneier, "Applied Cryptography", pp. 346ff, "Theory of Block Cipher Design".

The obvious problem with the latter option is that, whist standard block ciphers are generally based on common general principles, they adopt particular design decisions that have been subject to considerable scrutiny; yours presumably won't be.
I would also recommend standing back a bit from the problem (or perhaps explaining a bit more what you're trying to do), because it seems to be based on requirements that would normally go against good security practice (having the same plaintext always encrypt to the same ciphertext is something one would normally specifically avoid, for example). So you could have the best designed Feistel cipher in the world, but introduce some other vulnerability in how you're using it.
[*] TripleDES is generally not recommended because AES gives better security more efficiently (you might like to see some comparative timings of block ciphers that I took in Java to see just how bad it is). However, this might not matter in your particular application.
No, just "pad" your data out with some bytes you don't care about (but which are always the same if that's your requirement) so that you reach the size of a block. (If you're using an appropriate padding mode, then this will be done for you.)

A: I believe this is what you are looking for
http://web.cs.ucdavis.edu/~rogaway/papers/shuffle.html
This algorithm lets you construct PRP (i.e. arbitrary length block cipher) from secure PRF (e.g. sha256, blake2)
Block cipher in CTR mode has the same issue as a stream cipher.
Without a proper MAC (which require more bytes added) it will susceptible to bit flipping.
And without unique IV (which also require more bytes added) it will be just a broken implementation.

A: You can use a stream cipher only, if you have a unique salt for every encryption (don't even think about re-using the same salt, as that would be trivial to break).
When you have such unique values (e. g. a sequence number that's already associated with your values), you can use e.g. the stream cipher RC4-drop.
When you don't have such unique numbers already, you probably can't use a stream cipher, because you only have 48 bits for your result (so no space left for the salt.)
As for a block cipher with 48 bits - sorry, I don't know such a cipher, either. Maybe what you can do, is combining four 48 bit values into a 192 bit value, resulting in three 64 bit blocks, encode them, and then split them into four 48 bit values again. (I have no idea, if that would be possible in your situation or not?)

A: If you have a unique counter / sequence number associated with each plaintext value, then you can just use any block cipher in CTR (counter) mode.
To encrypt value V that is sequence number N under key K:

*

*Expand N to the size of a block;

*Encrypt N with the block cipher and key K;

*Take the first 48 bits of the result and XOR them with V.

Decryption is the same.  The most important thing to remember with this method is:
Never, ever use the same key and sequence number to encrypt two different values.
Sequence numbers must be unique.  If your sequence restarts, you must use a new key.

A: There is a 48-bit block 80-bit key cipher designed in 2009 - KATAN48 (the family version of KTANTAN48 has some key scheduling issue. So far, it was not broken, and has quite high security margins, so it has passed the test of time.

A: Here's a proposed solution that meets both of your requirements.
What if you use a cipher with a 32-bit block size (such as Skip32) and run it twice, as described below.
You have a 48-bit value to encode, for example:
f2800af40110

Step 1:
Split this into a 32-bit value and a 16-bit value using some method. Here we'll just grab the left 4 bytes and the right 2 bytes (but in practice you could use a secret bitmask, see below).
32-bit value: f2800af4
16-bit value: 0110

Step 2:
Encrypt the first one with a secret key K1, using Skip32 and let's say we get:
Encrypted 32-bit value: b0daf2b9

Step 3:
Split this into two 16-bit values (again you could use a secret bitmask, but for this example we'll grab the left/right two bytes).
Value 1: b0da
Value 2: f2b9

Step 4:
Combine value 1 with the the 16-bit value from step 1 to get a new 32-bit value:
b0da0110

Step 5:
Encrypt the resulting 32-bit value with secret key K2, again using Skip32:
Encrypted 32-bit value: 6135d8f4

Step 6:
Combine this 32-bit value with value 2 from step 3 to get a 48-bit encrypted result.
6135d8f4f2b9

The result is both deterministic and reversible. No two inputs will produce the same output.
Note on splitting/combining values
Steps 1 and 3 above will split a value in a predictable way. I'm not sure if this introduces any weakness, but one alternative is to use a bitmask. If we want to split a 48-bit input number into 32-bits and 16-bits, we could come up with a bitmask, essentially a number with 16 1's that can dictate how we split bits of the input number to get two output numbers, as follows:
INPUT  : 111100101000000000001010111101000000000100010000
BITMASK: 001010111001110000100000010001100000011001100000
           | | |||  |||    |      |   ||      ||  ||
VALUE 1:   1 0 101  000    0      1   10      00  00      => a860
VALUE 2: 11 1 0   00   0000 010101 110  000000  10  10000 => e015c050

Similarly for steps 4 and 6 you could combine two values by interleaving bits based on a bitmask.
If you use separate bitmasks for each step and separate keys for each step you end up with 2 keys and 4 bitmasks, all of which would be needed to encrypt/decrypt values.
Quick note on Skip32 and it's use cases
"The Skip32 has the uncommon properties of being fast, creating very dissimilar encrypted values for consecutive input values, and producing output of the same size as the input. These make this cipher particularly useful for obfuscating series of sequential integers (e.g. auto-incremented database ids)."
- https://docs.rs/skip32/1.0.5/skip32/
Any thoughts about this approach from someone more experienced with cryptography than I am?

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